Three-dimensional representation method and an apparatus thereof

ABSTRACT

A three-dimensional representation method for generating a three-dimensional image by displaying two-dimensional images on a plurality of image planes located at different depth positions wherein two-dimensional images are generated in which an object to be presented is projected, along the line of sight of an observer, onto the plurality of image planes located at different depth positions as seen from the observer, the brightness levels of the generated two-dimensional images are changed individually for each image plane and the generated two-dimensional images are displayed on the plurality of image planes.

[0001] This application is based on Patent Application Nos. 139602/1998filed on May 21, 1998 in Japan, 262804/1998 filed on Sep. 17, 1998 inJapan, 280739/1998 filed on Oct. 2, 1998 in Japan, 304374/1998 filed onOct. 26, 1998 in Japan, 326931/1998 filed on Nov. 17, 1998 in Japan and60393/1999 filed on Mar. 8, 1999 in Japan, the content of which isincorporated hereinto by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a three-dimensionalrepresentation method and an apparatus capable of electronicallyreproducing a moving picture or video with a reduced amount ofinformation on a three-dimensional image.

[0004] 2. Description of the Prior Art

[0005] A liquid crystal shutter eyeglasses system shown in FIG. 1 iswell known as a conventional system which is electrically rewritable,has a small amount of information and can display a three-dimensionalvideo.

[0006] The working principle of the liquid crystal shutter eyeglassessystem will be explained below.

[0007] In this liquid crystal shutter eyeglasses system, athree-dimensional object α1 is shot by cameras (α2, α3) from differentdirections to generate images (parallactic images) representing thethree-dimensional object α1 as viewed from different directions.

[0008] The images taken by the cameras (α2, α3) are combined by a videosignal converter α4 into a single video signal and fed into atwo-dimensional display (for example, CRT display) α5.

[0009] An observer α7 views an image on the two-dimensional display α5by wearing liquid crystal shutter eyeglasses α6.

[0010] Here, when the two-dimensional display α5 is displaying an imagefrom the camera α3, the liquid crystal shutter eyeglasses α6 are madeopaque on the left side and transparent on the right side. When thetwo-dimensional display α5 is displaying an image from the camera α2,the liquid crystal shutter eyeglasses α6 are made transparent on theleft side and opaque on the right side.

[0011] By switching the above operations at high speed, the viewer feelshe is watching parallactic images with both eyes because of the afterimage effect and therefore can see the object three-dimensionallybecause of binocular parallax.

[0012] Further, a volumetric system as shown in FIGS. 2A and 2B has beenproposed as one of the conventional systems that are electricallyrewritable, have a small amount of information and can display athree-dimensional video.

[0013] The working principle of this volumetric system is explained inthe following.

[0014] In the volumetric type, as shown in FIG. 2B, a three-dimensionalobject β1 is sampled in the direction of depth as seen from the viewerto generate a set of two-dimensional images β2, which is reproduced in adepth direction on a time division basis on a volumetricthree-dimensional display β3 to display a reproduced three-dimensionalimage β4.

[0015] The liquid crystal shutter eyeglasses system shown in FIG. 1,however, has a drawback that because of the required use of the liquidcrystal shutter eyeglasses α6, the system, when used forteleconferencing, looks very unnatural.

[0016] Further, there are large inconsistencies among binocularparallax, convergence and focusing, which are physiological factors ofstereoscopy.

[0017] That is, in the liquid crystal shutter eyeglasses system shown inFIG. 1, although the requirements of binocular parallax and convergenceare almost met, this system will cause eyestrain because the focal planeis on the display surface.

[0018] In the volumetric type shown in FIGS. 2A and 2B, the depthpositions of the reproduced three-dimensional object β1 are close to thesurfaces on which images are actually displayed, and are also disposedbetween these surfaces, so that unlike the liquid crystal shuttereyeglasses system, this volumetric system can suppress contradictionsamong binocular parallax, convergence and focusing.

[0019] With the volumetric system, however, because the depth positionsof the reproduced images are discrete, it is difficult to reproduce athree-dimensional object located at an intermediate position between thediscreet display positions, or a three-dimensional object that variesgreatly in the depth direction.

SUMMARY OF THE INVENTION

[0020] It is an object of the present invention to provide athree-dimensional representation method and apparatus capable ofdisplaying a video without requiring a viewer to wear glasses.

[0021] Another object of the invention is to provide a three-dimensionalrepresentation method and apparatus which can suppress contradictionsamong physiological factors for stereoscopy.

[0022] Another object of the invention is to provide a three-dimensionalrepresentation method and apparatus which can be electrically erased andprogrammed.

[0023] These and other objects and novel features of the invention willbecome apparent from the following descriptions in this specificationand accompanying drawings.

[0024] Representative aspects of the present invention may be brieflysummarized as follows.

[0025] This invention is characterized by a three-dimensionalrepresentation method for generating a three-dimensional image bydisplaying two-dimensional images on a plurality of image planes locatedat different depth positions, the method comprising the steps of:generating two-dimensional images by projecting an object to bepresented, along the line of sight of an observer, onto a plurality ofimage planes located at different depth positions as seen from theobserver; and changing brightness levels of the generatedtwo-dimensional images individually for each image plane and displayingthe generated two-dimensional images on the plurality of image planes.

[0026] According to the invention, when the object to be presented isdisplayed at a depth position close to the observer, the brightnesslevels of the two-dimensional images displayed on those image planes ofthe plurality of image planes which are close to the observer may beraised and the brightness levels of the two-dimensional images displayedon the image planes remote from the observer may be lowered. When theobject to be presented is displayed at a depth position remote from theobserver, the brightness levels of the two-dimensional images displayedon those image planes of the plurality of image planes which are closeto the observer may be lowered and the brightness levels of thetwo-dimensional images displayed on the image planes remote from theobserver may be raised.

[0027] The two-dimensional images are displayed on the plurality ofimage planes in such a way that the two-dimensional images overlap eachother when the two-dimensional images are viewed from one point on aline which passes through the right and left eyes of an observer, andthat an overall brightness level as seen by the observer is equal to thebrightness level of the original object to be presented.

[0028] According to the invention, the two-dimensional images arearranged to overlap by viewing from one point on the line which passesthrough the right and left of the observer and the two-dimensionalimages are enlarged or reduced in the horizontal direction respectively.

[0029] According to the invention, the two-dimensional images may beswitched successively to generate a three-dimensional moving image.

[0030] According to the invention, when the two-dimensional imagesinclude a plurality of images of an object moving in a direction ofdepth and the object is moving toward the observer, the brightnesslevels of the object images displayed on the plurality of image planesmay be progressively raised toward an image plane close to the observerand progressively lowered toward an image plane remote from the observerin synchronism with the successive switching of the two-dimensionalimages, and when the two-dimensional images include a plurality ofimages of an object moving in a direction of depth and the object ismoving away from the observer, the brightness levels of the objectimages displayed on the plurality of image planes may be progressivelylowered toward an image plane close to the observer and progressivelyraised toward an image plane remote from the observer in synchronismwith the successive switching of the two-dimensional images.

[0031] According to the invention, a three-dimensional display maycomprise: a first means for generating two-dimensional images byprojecting an object to be presented, along the line of sight of anobserver, onto a plurality of image planes located at different depthpositions as seen from the observer; a second means for displaying thetwo-dimensional images generated by the first means on the plurality ofimage planes located at different depth positions as seen from theobserver; and a third means for changing brightness levels of thetwo-dimensional images displayed on the plurality of image planesindividually for each image plane.

[0032] According to the invention, the second means may comprise: aplurality of two-dimensional displays; and partial reflecting mirrorscombined with the plurality of two-dimensional displays except for onetwo-dimensional display located at the remotest depth position from theobserver, the partial reflecting mirrors being adapted to locate imagesof the two-dimensional displays on the line of sight of the observer.

[0033] According to the invention, the second means may comprise: aplurality of two-dimensional displays; and combinations of partialreflecting mirrors and lenses, the partial reflecting mirror and lenscombinations being combined with the plurality of two-dimensionaldisplays except for one two-dimensional display located at the remotestdepth position from the observer, the partial reflecting mirror and lenscombinations being adapted to locate images of the two-dimensionaldisplays on the line of sight of the observer.

[0034] According to the invention, the second means may comprise: aplurality of two-dimensional displays; a total reflecting mirror orpartial reflecting mirror combined with one of the plurality oftwo-dimensional displays which is located at the remotest depth positionfrom the observer, the total reflecting mirror or partial reflectingmirror being adapted to locate an image of the one two-dimensionaldisplay on the line of sight of the observer; and partial reflectingmirrors combined with the two-dimensional displays except for the onetwo-dimensional display located at the remotest depth position from theobserver, the partial reflecting mirrors being adapted to locate imagesof the two-dimensional displays on the line of sight of the observers.

[0035] According to the invention, the second means may comprise: aplurality of two-dimensional displays; a combination of a totalreflecting mirror and a lens or a combination of a partial reflectingmirror and a lens, the combination being combined with one of theplurality of two-dimensional displays which is located at the remotestdepth position from the observer, the combination being adapted tolocate an image of the one two-dimensional display on the line of sightof the observer; and combinations of partial reflecting mirrors andlenses, the combinations being combined with the two-dimensionaldisplays except for one two-dimensional display located at the remotestdepth position from the observer, the combinations being adapted tolocate images of the two-dimensional displays on the line of sight ofthe observer.

[0036] According to the invention, the second means may comprise: aplurality of scatter plates capable of controlling a switching between atransmitting state and a scattering state or a plurality of reflectionplates capable of controlling the switching between a reflecting stateand a transmitting state, the scatter plates or reflection plates beinglocated at different depth positions as viewed from the observer; aplurality of projection type two-dimensional displays for projectingtwo-dimensional images onto the plurality of scatter plates or theplurality of reflection plates; and a plurality of shutters disposedbetween the plurality of scatter plates or reflection plates and theplurality of projection type two-dimensional displays, the plurality ofshutters being adapted to switch between a transmitting state and acutoff state in synchronism with the switching between the transmittingstate and the scattering state of the plurality of scatter plates orbetween the reflecting state and the transmitting state of the pluralityof reflection plates.

[0037] According to the invention, a lens optical system may be disposedbetween the observer and the plurality of image planes located atdifferent depth positions as seen from the observer.

[0038] According to the invention, the second means may comprise atwo-dimensional display, an optical system, and a varifocal mirror.

[0039] According to the invention, the second means may comprise: avibration screen which vibrates in the direction of depth; an opticalsystem including a lens; a scanning means for raster-scanning a laserbeam; and a laser beam source.

[0040] According to the invention, the second means may comprise: an LEDdisplay having an LED array; a parallel advancing/rotating device forparallelly advancing/rotating the LED display; and a video feedingdevice for feeding a video signal to the LED display.

[0041] According to the invention, the second means may comprise: a filmhaving a two-dimensional image recorded therein or two-dimensionaldisplay; an image transforming optical system having a prism or mirror;and a projection drum.

[0042] According to the invention, the second means may successivelyswitch the two-dimensional images generated by the first means togenerate a moving three-dimensional image.

[0043] According to the invention, when the two-dimensional imagesgenerated by the first means include a plurality of images of an objectmoving in a direction of depth and the object is moving toward theobserver, the third means may progressively raise the brightness levelsof the object images displayed on the plurality of image planes towardan image plane close to the observer and progressively lower thebrightness levels of the object images toward an image plane remote fromthe observer in synchronism with the successive switching of thetwo-dimensional images by the second means, and when the object ismoving away from the observer, the third means may progressively lowerthe brightness levels of the object images displayed on the plurality ofimage planes toward an image plane close to the observer andprogressively raise the brightness levels of the object images toward animage plane remote from the observer in synchronism with the successiveswitching of the two-dimensional images by the second means.

[0044] The above and other objects, effects, features and advantages ofthe present invention will become more apparent from the followingdescription of embodiments thereof taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0045]FIG. 1 is a schematic configuration of a conventionalthree-dimensional display;

[0046]FIGS. 2A and 2B are schematic configurations of anotherconventional three-dimensional display;

[0047]FIG. 3 is a schematic diagram showing the principle of athree-dimensional display according to a first embodiment of the presentinvention;

[0048]FIG. 4 is a schematic diagram showing the principle of athree-dimensional display according to the first embodiment;

[0049]FIG. 5 is a schematic diagram showing the principle of athree-dimensional display according to the first embodiment;

[0050]FIG. 6 is a schematic diagram showing the principle of athree-dimensional display according to the first embodiment;

[0051]FIG. 7 is a schematic diagram showing the principle of athree-dimensional display according to the first embodiment;

[0052]FIG. 8 is a schematic diagram showing the principle of athree-dimensional display according to the first embodiment;

[0053]FIGS. 9A and 9B are schematic diagrams showing the principle of athree-dimensional display according to the first embodiment;

[0054]FIGS. 10A and 10B are schematic diagrams showing the principle ofa three-dimensional display according to the first embodiment;

[0055]FIG. 11 is a schematic diagram showing the principle of athree-dimensional display according to a second embodiment;

[0056]FIG. 12 is a schematic diagram showing the principle of athree-dimensional display according to the second embodiment;

[0057]FIG. 13 is a schematic diagram showing the principle of athree-dimensional display according to the second embodiment;

[0058]FIG. 14 is a schematic diagram showing the principle of athree-dimensional display according to the second embodiment;

[0059]FIG. 15 is a schematic diagram showing the principle of athree-dimensional display according to the second embodiment;

[0060]FIG. 16 is a schematic diagram showing the principle of athree-dimensional display according to the second embodiment;

[0061]FIGS. 17A and 17B are schematic diagrams showing the outlineconfiguration of a three-dimensional display according to a thirdembodiment of the invention;

[0062]FIGS. 18A and 18B are schematic diagrams showing examples thatallow flexible changes in the position of an image plane byincorporating a lens or the like in an optical system of the thirdembodiment;

[0063] FIGS. 19 is a schematic diagram showing an example in which thereis an increased number of two-dimensional displays, according to thethird embodiment;

[0064]FIG. 20 is a schematic diagram showing an example which uses aplurality of projector type two-dimensional displays of the thirdembodiment and scatter plates to form an optical system that projectsimages from the projectors onto the scatter plates;

[0065]FIG. 21 is a schematic diagram showing another example which addsoptical devices to the third embodiment;

[0066]FIG. 22 is a schematic diagram showing the outline configurationof a varifocal mirror type volumetric three-dimensional displayaccording to a fourth embodiment of the invention;

[0067]FIG. 23 is a schematic diagram showing the outline configurationof a vibration screen type volumetric three-dimensional displayaccording to the fourth embodiment;

[0068]FIG. 24 is a schematic diagram showing the outline configurationof a rotary LED type three-dimensional display according to a fifthembodiment of the invention;

[0069]FIG. 25 is a schematic diagram showing the outline configurationof a synthalyzer type three-dimensional display according to a sixthembodiment of the invention;

[0070]FIGS. 26A and 26B are conceptual diagrams showing the outlineconfigurations of the three-dimensional display according to a seventhembodiment of the invention;

[0071]FIG. 27 is a conceptual diagram showing how a distribution deviceworks according to this embodiment;

[0072]FIGS. 28A to 28C are conceptual diagrams showing how images aremoved according to this embodiment;

[0073]FIGS. 29A and 29B are schematic diagrams showing a method ofmoving images according to this embodiment;

[0074]FIGS. 30A and 30B are schematic diagrams showing a method ofmoving the displays according to this embodiment;

[0075]FIG. 31 is a schematic diagram showing a method of moving thewhole apparatus according to this embodiment;

[0076]FIGS. 32A to 32C are schematic diagrams showing a positiondetection method according to this embodiment;

[0077]FIGS. 33A and 33B are schematic diagrams showing another positiondetection method according to this embodiment;

[0078]FIG. 34 is a block diagram showing the concept of athree-dimensional display according to an eighth embodiment of theinvention;

[0079]FIGS. 35A to 35D are schematic diagrams showing the principle ofthe three-dimensional display according to the eighth embodiment;

[0080]FIG. 36 is a schematic diagram showing the outline configurationof the three-dimensional display according to the eighth embodiment;

[0081]FIG. 37 is a schematic diagram showing the outline configurationof a three-dimensional display according to a ninth embodiment of theinvention;

[0082]FIG. 38 is a schematic diagram showing the outline configurationof a three-dimensional display according to a tenth embodiment of theinvention;

[0083]FIG. 39 is a schematic diagram showing the outline configurationof a three-dimensional display according to an eleventh embodiment ofthe invention;

[0084]FIG. 40 is a schematic diagram showing the outline configurationof a three-dimensional display according to a twelfth embodiment of theinvention;

[0085]FIG. 41 is a schematic diagram showing the outline configurationof a three-dimensional display according to a thirteenth embodiment ofthe invention;

[0086]FIG. 42 is a schematic diagram showing the outline configurationof a three-dimensional display according to a fourteenth embodiment ofthe invention;

[0087]FIG. 43 is a schematic diagram showing the method of generatingtwo-dimensional images in the three-dimensional display according to thefourteenth embodiment;

[0088]FIG. 44 is a schematic diagram showing the correspondence betweenpixels of a two-dimensional display and polarization varying elements ofa polarization varying device in the three-dimensional display accordingto the fourteenth embodiment;

[0089]FIG. 45 is a schematic diagram showing the correspondence betweenpixels of a two-dimensional display and polarization varying elements ofa polarization varying device in the three-dimensional display accordingto the fourteenth embodiment;

[0090]FIG. 46 is a schematic diagram showing a method of displaying athree-dimensional image in the three-dimensional display according tothe fourteenth embodiment;

[0091]FIG. 47 is a schematic diagram showing a method of displaying athree-dimensional image in the three-dimensional display according tothe fourteenth embodiment;

[0092]FIG. 48 is a schematic diagram showing a method of displaying athree-dimensional image in the three-dimensional display according tothe fourteenth embodiment;

[0093]FIG. 49 is a schematic diagram showing a method of displaying athree-dimensional image in the three-dimensional display according tothe fourteenth embodiment;

[0094]FIG. 50 is a schematic diagram showing the outline configurationof a three-dimensional display according to a fifteenth embodiment ofthe invention;

[0095]FIGS. 51A and 51B are schematic diagrams showing a method ofdisplaying a three-dimensional image in the three-dimensional displayaccording to the fifteenth embodiment;

[0096]FIG. 52 is a schematic diagram showing one example of a polarizingtype bifocal optical system that can be used in the three-dimensionaldisplay according to each of the embodiments of the invention;

[0097]FIG. 53 is a schematic diagram showing the relation betweenincoming light and exit light in the polarizing type bifocal opticalsystem shown in FIG. 52;

[0098]FIG. 54 is a schematic diagram showing another example of apolarizing type bifocal optical system that can be used in thethree-dimensional display according to each of the embodiments of theinvention;

[0099]FIG. 55 is a schematic diagram showing still another example of apolarizing type bifocal optical system that can be used in thethree-dimensional display according to each of the embodiments of theinvention;

[0100]FIG. 56 is a schematic diagram showing an optical system that canbe used instead of the polarizing beam splitter shown in FIG. 55;

[0101]FIG. 57 is a cross-sectional view showing the outlineconfiguration of a twisted nematic type polarization varying device thatcan be used in the three-dimensional display according to each of theembodiments of the invention;

[0102]FIG. 58 is a schematic diagram showing the operating principle ofthe twisted nematic type polarization varying device shown in FIG. 57;

[0103]FIG. 59 is a cross-sectional view showing the outlineconfiguration of an in-plane type polarization varying device that canbe used in the three-dimensional display according to each of theembodiments of the invention;

[0104]FIG. 60 is a schematic diagram showing the working principle ofthe in-plane type polarization varying device shown in FIG. 59;

[0105]FIG. 61 is a schematic diagram showing the outline configurationof a homogeneous type polarization varying device that can be used inthe three-dimensional display according to each of the embodiments ofthe invention;

[0106]FIGS. 62A to 62C are schematic diagrams showing light incident onthe homogeneous type polarization varying device shown in FIG. 61 and anorientation of an alignment layer;

[0107]FIGS. 63A and 63B are schematic diagrams showing the operatingprinciple of the homogenous type polarization varying device shown inFIG. 61;

[0108]FIG. 64 is a schematic diagram showing the principle of ahead-mounted display according to a nineteenth embodiment of theinvention;

[0109]FIG. 65 is a schematic diagram showing a method of generatingtwo-dimensional images in the head-mounted display according to thenineteenth embodiment;

[0110]FIG. 66 is a schematic diagram showing a method of displaying athree-dimensional image in the head-mounted display according to thenineteenth embodiment;

[0111]FIG. 67 is a schematic diagram showing a method of displaying athree-dimensional image in the head-mounted display according to thenineteenth embodiment;

[0112]FIG. 68 is a schematic diagram showing a method of displaying athree-dimensional image in the head-mounted display according to thenineteenth embodiment;

[0113]FIG. 69 is a schematic diagram showing a method of displaying athree-dimensional image in the head-mounted display according to thenineteenth embodiment;

[0114]FIG. 70 is a schematic diagram showing the principle of ahead-mounted display according to a twentieth embodiment of theinvention;

[0115]FIG. 71 is a schematic diagram showing a method of generatingtwo-dimensional images in the head-mounted display according to thetwentieth embodiment;

[0116]FIG. 72 is a schematic diagram showing a method of displayingthree-dimensional images in the head-mounted display according to thetwentieth embodiment;

[0117]FIG. 73 is a schematic diagram showing a method of displayingthree-dimensional images in the head-mounted display according to thetwentieth embodiment;

[0118]FIG. 74 is a schematic diagram showing a method of displayingthree-dimensional images in the head-mounted display according to thetwentieth embodiment;

[0119]FIG. 75 is a schematic diagram showing a method of displayingthree-dimensional images in the head-mounted display according to thetwentieth embodiment;

[0120]FIG. 76 is a schematic diagram showing one example of an opticalsystem that can be used in each of the embodiments of the invention;

[0121]FIG. 77 is a schematic diagram showing another example of anoptical system that can be used in each of the embodiments of theinvention;

[0122]FIG. 78 is a schematic diagram showing a further example of anoptical system that can be used in each of the embodiments of theinvention;

[0123]FIG. 79 is a schematic diagram showing a further example of anoptical system that can be used in each of the embodiments of theinvention;

[0124]FIG. 80 is a schematic diagram showing a further example of anoptical system that can be used in each of the embodiments of theinvention;

[0125]FIGS. 81A and 81B are schematic diagrams showing three-dimensionaldisplays according to a twenty-second embodiment of the invention;

[0126]FIGS. 82A and 82B are schematic diagrams showing three-dimensionaldisplays according to a twenty-third embodiment of the invention;

[0127]FIGS. 83A and 83B are schematic diagrams showing three-dimensionaldisplays according to a twenty-fourth embodiment of the invention;

[0128]FIGS. 84A to 84E are schematic diagrams showing three-dimensionaldisplays according to a twenty-fifth embodiment of the invention;

[0129]FIGS. 85A and 85D are schematic diagrams showing three-dimensionaldisplays according to a twenty-sixth embodiment of the invention;

[0130]FIGS. 86A to 86D are schematic diagrams showing three-dimensionaldisplays according to a twenty-seventh embodiment of the invention;

[0131]FIGS. 87A and 87B are schematic diagrams showing three-dimensionaldisplays according to a twenty-eighth embodiment of the invention;

[0132]FIGS. 88A to 88C are schematic diagrams showing the principle ofthe invention;

[0133]FIG. 89 is a schematic diagram showing the principle of theinvention;

[0134]FIGS. 90A and 90B are schematic diagrams showing the principle ofthe invention; and

[0135]FIGS. 91A and 91B are schematic diagrams showing athree-dimensional representation method according to a furtherembodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0136] The present patent application claims the priority from JapanesePatent Application Nos. 139602/1998, 262804/1998, 280739/1998,304374/1998, 326931/1998 and 60,393/1999 filed with the Japanese PatentOffice. The Japanese Patent Application No. 326931/1998 has followed thenecessary procedure in claiming the priority in Japan from the JapanesePatent Application No. 139602/1998.

[0137] Therefore, embodiments described in this specification use, atparagraphs that contain the same descriptions of the above patentapplications, the corresponding paragraph numbers used in theseapplications. The paragraph numbers used in this specification areassigned with symbols as shown in a table below to distinguish betweenthe applications. It should also be noted that descriptions under theassigned paragraph numbers use different drawing numbers and referencenumbers from those of the above patent applications in order to makethem distinguishable. TABLE 1 Symbol Application number A 326931/1998(including 139602/1998) B 262804/1998 C 280739/1998 D 304374/1998 B 60393/1999 F New matters

[0138] Now, by referring to the accompanying drawings, embodiments ofthe present invention will be described in detail.

[0139] Throughout the drawings, parts having the same functions areassigned like reference numbers and their explanations are not repeated.

[0140] In the description of the embodiments, a word “plane” on which toput an image is used. This is similar in meaning to an image plane thatis often used in optics. Means to realize such an image plane canobviously be realized by combining many optical devices, which include avariety of optical elements, such as lens, total reflecting mirror,partial reflecting mirror, curved mirror, prism, polarizer andwavelength plate, and two-dimensional displays, such as CRT (cathode raytube), liquid crystal display, LED (light emitting diode) display,plasma display, FED (field emission display), DMD (digital mirrordisplay), projection type display and line drawing type display.

[0141] Although this specification deals mainly with a case where athree-dimensional object is represented as two-dimensional imagesdisplayed on two planes, it is obvious that the similar effect can beexpected when two or more planes are used.

[0142] [A-0012]

[0143] [Embodiment 1]

[0144]FIG. 3 and FIGS. 10A and 10B are schematic views for explainingthe principle of a three-dimensional display according to a firstembodiment of the present invention.

[0145] As shown in FIG. 3, a plurality of planes, such as planes 101,102 (plane 101 is closer to the observer 100 than plane 102) areprovided in front of an observer 100. To display a plurality oftwo-dimensional images on these planes an optical system 103 isconstructed by using two-dimensional displays and a variety of opticalelements (details will be given later).

[0146] Examples of the two-dimensional displays may include CRT, liquidcrystal display, LED display, plasma display, FED display, projectiontype display and line drawing type display, and examples of the opticalelements may include lens, total reflecting mirror, partial reflectingmirror, curved mirror, prism, polarizer and wavelength plate.

[0147] Then, as shown in FIG. 4, a three-dimensional object 104, whichis to be presented to the observer 100, is projected onto the planes101, 102 to generate images 105, 106 (hereinafter referred to astwo-dimensional images).

[0148] The two-dimensional images can be formed by a variety of ways,which include a technique that uses two-dimensional images formed byphotographing the object 104 by camera along the line of sight; atechnique that synthesizes a plurality of two-dimensional images shotfrom different directions; or synthesizing and modeling techniques basedon computer graphics.

[0149] As shown in FIG. 3, these two-dimensional images 105, 106 aredisplayed on the planes 101, 102 respectively so that they overlap eachother by viewing from one point on the line of which passes through theright and left eyes of the observer 100.

[0150] This can be achieved by placing the centers or gravity centers ofthe two-dimensional images 105, 106 and by controlling a ratio ofenlargement/reduction of each image.

[0151] [A-0013]

[0152] An important point of this embodiment is that, in the apparatuswith the above configuration, the brightness of each of the images 105,106 is changed according to the depth position of the three-dimensionalobject 104 while keeping constant the overall brightness as seen by theobserver 100.

[0153] One example method of changing the brightness is explained asfollows.

[0154] Here, since the drawings are monochrome, in following drawings, apart having high value in brightness is shown with high density exceptfor FIGS. 10A and 10B

[0155] When for example the three-dimensional object 104 is on the plane101, the brightness of the two-dimensional image 105 on this plane isset equal to the brightness of the three-dimensional object 104 and thebrightness of the two-dimensional image 106 is set to zero, as shown inFIG. 5.

[0156] Next, when for example the three-dimensional object 104 isslightly moved away from the observer 100 and is located at a positionslightly away from the plane 101 and closer to the plane 102, thebrightness of the two-dimensional image 105 is slightly lowered and thebrightness of the two-dimensional image 106 is slightly raised, as shownin FIG. 6.

[0157] When for example the object 104 is moved further away from theobserver 100 and is located at a position further away from the plane101 and closer to the plane 102, the brightness of the two-dimensionalimage 105 is further lowered and the brightness of the two-dimensionalimage 106 is further raised, as shown in FIG. 7.

[0158] When the object 104 is on the plane 102, the brightness of thetwo-dimensional image 106 is set equal to the brightness of the object104 and the brightness of the two-dimensional image 105 is set to zero,as shown in FIG. 8.

[0159] By displaying in this manner, the observer 100 is made to feel asif the object 104 is located between the planes 101 and 102 because ofobserver's physiological or mental factors or optical illusion althoughwhat is actually shown to the observer is the two-dimensional images105, 106.

[0160] That is, when for example the two-dimensional images 107, 108with almost equal brightness are displayed on the planes 101 and 102,the object 104 looks as if it lies near to a middle point between thedepth positions of the planes 101, 102.

[0161] [A-0014]

[0162] Although the above description mainly concerns a method andapparatus which represents the depth position of the entirethree-dimensional object 104 by using two-dimensional images displayedon the planes 101, 102, for example, the first embodiment can apparentlybe used as a method and apparatus for showing the depth of athree-dimensional object itself.

[0163] One such example is described below.

[0164] First, the outline configuration of a three-dimensional displayaccording to this embodiment is as shown in FIG. 3, in which a pluralityof planes, for example planes 101, 102 (plane 101 is closer to anobserver 100 than plane 102), are set in front of the observer 100 andin which an optical system 103 is constructed by using, for example,two-dimensional displays and a variety of optical elements to display aplurality of two-dimensional images on these planes (details will begiven in third and subsequent embodiments).

[0165] Next, the three-dimensional object 104 to be presented to theobserver 100 is shot in the direction of the line of sight of both eyesof the observer 100 to generate, for instance, two-dimensional images105, 106.

[0166] These two-dimensional images 105, 106 are, as shown in FIG. 3,displayed on the planes 101 and 102 respectively such that they overlapeach other by viewing from the point on the line of which passes throughthe right and left eyes of the observer.

[0167] This can be realized by placing the centers or gravity centers ofthe two-dimensional images 105, 106 and by controlling a ratio ofenlargement/reduction of each image, as described earlier.

[0168] Position setting of each image and enlargement/reduction areexecuted by a computer connected with the two-dimensional displayapparatus.

[0169] An important point of this embodiment is that, in the apparatuswith the above configuration, the brightness of each part of each of theimages 105, 106 is changed according to the depth position of each partof the object 104 while keeping constant the overall brightness as seenby the observer 100.

[0170] One example method of changing the brightness will be explainedby referring to FIGS. 9A and 9B for a case where two display planes areused.

[0171] [A-0015]

[0172]FIG. 9A represents an example image displayed on a plane close tothe observer 100, for example, on the plane 101, and FIG. 9B representsan example image displayed on a plane remote from the observer 100, forexample, on the plane 102.

[0173] Referring to FIGS. 9A and 9B that show a cake as an object, upperand lower surfaces of the cake (object) are almost flat, except for thecandles stuck on the top, the wall surface is cylindrical, and thecandles are arranged near the circumference of the upper surface of thecake.

[0174] In the two-dimensional images 105, 106 in this case, on the upperand lower surfaces the upper parts represent the remote parts of thecake. On the wall surface, the central part of the wall surfacecorresponds to the near side of the cake, and as you go from the centertoward the left and right, the surface position moves toward the farside. And the central part of the hidden wall surface, which is shownhigher than the front wall surface, is located on the far side.

[0175] In this case, the brightness on the upper and lower surfaces isprogressively changed according to the depth position so that, as shownin FIG. 9A, on a plane close to the observer 100, or the plane 101, aportion close to the observer 100 (a lower part of the two-dimensionalimage) has a higher brightness level and a portion remote from theobserver (an upper part of the two-dimensional image) has a lowerbrightness level.

[0176] Further, on a plane remote from the observer, or the plane 102,the brightness is progressively changed according to the depth positionso that, as shown in FIG. 9B, a portion close to the observer (a lowerpart of the two-dimensional image) has a lower brightness level and aportion remote from the observer (an upper part of the two-dimensionalimage) has a higher brightness level.

[0177] Next, the brightness of the cylindrical portion is also changedprogressively according to its depth position so that, on a plane closeto the observer 100, or the plane 101, a portion close to the observer100 (around the center) has a higher brightness level and a portionremote from the observer (the near left and right end) has a lowerbrightness level, as shown in FIG. 9A.

[0178] On a plane remote from the observer 100, or the plane 102, thebrightness is changed progressively so that, as shown in FIG. 9B, aportion close to the observer 100 (around the center) has a lowerbrightness level and a portion remote from the observer (the near leftand right end) has a higher brightness level.

[0179] By displaying in this manner, the observer 100 is made to feel asif there is a cylindrical cake with almost flat top and bottom surfacesbecause of observer's physiological or mental factors or opticalillusion although what is actually shown to the observer istwo-dimensional images.

[0180] Although this embodiment has taken as an example a cylindricalobject with almost flat top and bottom surfaces, it is apparent that thesimilar effect can be obtained if the object has other shapes.

[0181] [A-0016]

[0182] In the embodiment 1, we have explained a case where thebrightness of the two-dimensional images displayed on two or more planesare changed while keeping the overall brightness as seen by the observer100 constant.

[0183] However, progressively lowering the overall brightness as seen bythe observer 100 toward the rear to emphasize the solidity of the objectis a common used technique in computer graphics. It is obvious that theuse of this technique also in this invention can promote the effect ofthe invention. One such example is shown in FIGS. 10A and 10B.

[0184] In FIG. 10A, the brightness of the floor is gradually loweredtoward the upper part of the Figure to make one feel as if the floorshown at the upper part of the Figure lies remote from the viewer in thedepth direction.

[0185] In FIG. 10B, the brightness of a chain (circular objects), inaddition to the floor, is also lowered progressively toward the left toproduce an effect that makes one perceive that the chain on the leftside is far in the depth direction.

[0186] As the means for calculating the degree of such brightnessreduction, there are many methods available, including a method thatuses a formula B′=B×T0/T (T: distance from a viewing point, T0: distancefrom a viewing point to a reference plane) in calculating-the brightnessB′ that produces the above effect with respect to the object'sbrightness B.

[0187] [A-0017]

[0188] It is apparent that the two-dimensional image plane in theembodiment 1 does not have to be a flat plane and can take other formssuch as spherical, ellipsoidal or quadratic surfaces, or other complexcurved surfaces and produce the similar effect.

[0189] In the embodiment 1, because, unlike the conventional methodshown in FIG. 1, there are at least two image display planes on the nearand far sides of the optical illusion position, contradictions among thebinocular parallax, convergence and focusing—the problem experiencedwith the conventional method—can be suppressed greatly, which in turn isexpected to reduce eyestrains.

[0190] Since the focus position is fixed at a position where the viewerlooks at two or more planes at the same time, the problem of theconventional method is improved greatly.

[0191] In this case, it is necessary to determine the depth distances ofa plurality of the planes, the depth distances being within the rangewherein blurring of the images obtained when the focus point is adjustedat the position of the object to be displayed on the depth direction byviewing from the observer is less is less than one obtained when thefocus points are adjusted at the plurality of the planes.

[0192] Further, unlike the conventional method shown in FIG. 2, anobject that exists at an intermediate position between the image planes,too, looks three-dimensional to the viewer and therefore the system ofthis embodiment offers the advantage of realistic solidity, not the kindof solidity presented by gathering sheet-divided depths.

[0193] Further, because the embodiment 1 can also show an object presentbetween a plurality of planes, it offers the advantage of being able toreduce the amount of data greatly when performing a three-dimensionaldisplay.

[0194] Further, because the embodiment 1 takes advantage of humanphysiological or mental factors or optical illusion based only onbrightness changes of images, the embodiment does not require the use ofa coherent light source such as a laser and facilitates the colorstereoscopic image representation.

[0195] Further, since this invention does not include mechanical drivingparts, it can suitably reduce the weight of and improve the reliabilityof the apparatus.

[0196] The embodiment 1 mainly concerns a case where there are only twoplanes for displaying two-dimensional images and where an object to bepresented to the observer lies between the two planes. It is, however,apparent that the similar configuration can be employed if there aremore planes or the object to be presented is located at a differentposition.

[0197] Further, in this embodiment, it is also apparent that athree-dimensional video image can be displayed by successively changingtwo-dimensional images.

[0198] [N]

[0199] When the described two-dimensional images are displayed tooverlap by viewing from one point on the line which passes through theright and left eyes of the observer, in the case that especially, theone point between the right and left eyes of the observer is used as thepoint on the line which passes through the right and left eyes of theobserver, reliability for obtaining an effect of three-dimensionalconsciousness is become bigger.

[0200] If it says simply, the above effect is obtained in many people orin many cases.

[0201] Further, the center point between the right and left eyes of theobserver is used as the above one point, it is easy to obtain the aboveeffect and has a merit that a size of double images in the right andleft eyes generated by planes O1 and O2 becomes smaller.

[0202] It is useful for change a depth or an inclination of the objectto be recognized by enlarging or reducing the size of a horizontaldirection.

[0203] However, variety of the brightness in the two-dimensional imageshaving same colors is described, when a color of the object to bedisplayed is purple, the object is made by using (mixing) a red displayof one plane and a blue display of another plane, the brightness of thetwo planes being deferent.

[0204] This is useful for matching a back ground image with the objectin view of color matching when the color of the outline of the object isdifferent from the color of the object itself though each displaysprovides strange feeling.

[0205] For the purpose to obtain the above effect, it is important tohave a common area of depth of the distance between planes displayingthe above two-dimensional images, the common area being within the rangein case that the object is viewed by single eye at the position of theright eye or the left eye.

[0206] If there is not common area the obserber feels the object farfrom the planes.

[0207] [A-0018]

[0208] [Embodiment 2]

[0209] FIGS. 11 to 16 illustrate the principle of a three-dimensionaldisplay according to a second embodiment of the present invention.

[0210] In the three-dimensional display of the second embodiment, asshown in FIG. 11, a plurality of planes, such as planes 111 and 112(plane 111 is closer to an observer 110 than plane 112), are installedin front of the observer 110 and, to display a plurality oftwo-dimensional images on these planes, an optical system 113 isconstructed by using two-dimensional displays and various opticalelements.

[0211] Among the possible two-dimensional displays there are CRT, liquidcrystal display, LED display, plasma display, FED display, projectiontype display and line drawing type display. Examples of the opticalelements may include lens, total reflecting mirror, partial reflectingmirror, curved mirror, prism, polarizer and wavelength plate.

[0212] Then, as shown in FIG. 12, a three-dimensional object 114, whichis to be presented to the observer 110, is projected onto the planes111, 112 to generate images 115, 116 (two-dimensional images).

[0213] The two-dimensional images 115, 116 can be formed by a variety ofways, which include a technique that uses two-dimensional images formedby photographing the object 114 by camera along the line of sight; atechnique that synthesizes a plurality of two-dimensional images shotfrom different directions; or synthesizing and modeling techniques basedon computer graphics.

[0214] [A-0019]

[0215] As shown in FIG. 11, the two-dimensional images 115, 116 aredisplayed on the planes 111 and 112 respectively so that they overlapeach other on the line of sight of the observer (this can be achieved bylocating the centers or gravity centers of the two-dimensional images115, 116 on the line of sight).

[0216] An important point of this embodiment is that the brightness ofeach image 115, 116 is changed according to a change over time of thedepth position of the three-dimensional object 114 while keepingconstant the overall brightness as seen by the observer 110.

[0217] This is explained by taking an example case where thethree-dimensional object 114 moves from the plane 111 to the plane 112with elapse of time.

[0218] As shown in FIG. 13, when the three-dimensional object 114 is onthe plane 111, the brightness of the two-dimensional image 115 on theplane 111 is set equal to that of the three-dimensional object 114 andthe brightness of the two-dimensional image 116 on the plane 112 is setto zero.

[0219] Next, as shown in FIG. 14, when the three-dimensional object 114progressively moves slightly away from the observer 110 and inches fromthe plane 111 toward the plane 112 over time, the brightness of thetwo-dimensional image 115 is lowered slightly over time according to themovement in the depth position of the three-dimensional object 114 andat the same time the brightness of the two-dimensional image 116 isslightly raised over time.

[0220] Next, as shown in FIG. 15, when the three-dimensional object 114moves further away from the observer 110 and inches from the plane 111further toward the plane 112 over time, the brightness of thetwo-dimensional image 115 is lowered further over time according to themovement in the depth position of the three-dimensional object 114 andat the same time the brightness of the two-dimensional image 116 israised further over time.

[0221] When, as shown in FIG. 16, the three-dimensional object 114finally reaches the plane 112 over time, the brightness of thetwo-dimensional image 116 on the plane 112 is changed over time until itbecomes equal to the brightness of the three-dimensional object 114according to the movement in the depth position of the three-dimensionalobject 114 and at the same time the brightness of the two-dimensionalimage 115 on the plane 111 is changed over time until it becomes zero.

[0222] [A-0021]

[0223] By displaying in this manner, the observer 110 is made to feel asif the three-dimensional object 114 moves over time from the plane 111to the plane 112 in the direction of depth because of observer'sphysiological or mental factors or optical illusion although what isactually shown to the observer is two-dimensional images 115, 116.

[0224] While this embodiment describes a case where thethree-dimensional object 114 moves over time from the plane 111 to theplane 112, it is obvious that the similar display effect can also beproduced in cases where the object moves from an intermediate depthposition between the planes 111 and 112 to the plane 112, where it movesfrom the plane 111 to an intermediate depth position between the planes111 and 112, and where it moves from an intermediate position betweenthe planes 111 and 112 to another intermediate position between theplanes 111 and 112.

[0225] Although this embodiment has described a case where there areonly two planes on which to place two-dimensional images and thethree-dimensional object 114 to be presented to the observer 110 movesbetween the two planes, it is obvious that the similar configuration canbe employed and the similar effect expected even when the number oftwo-dimensional image display planes is more than two or when thethree-dimensional object being presented moves crossing a plurality ofplanes.

[0226] Although this embodiment has described a case where onethree-dimensional object 114 moves between two planes on whichtwo-dimensional images are displayed, it is obvious that when aplurality of three-dimensional objects move, i.e., when the displayedtwo-dimensional images each include a plurality of object images movingin different directions, the brightness of the object images displayedon the respective display planes needs only to be changed according tothe moving directions of the objects and the speeds of their movements.

[0227] [A-0022]

[0228] [Embodiment 3]

[0229]FIGS. 17A and 17B illustrate the outline configuration of athree-dimensional display according to a third embodiment of theinvention.

[0230] In the three-dimensional display of the third embodiment, asshown in FIG. 17A, a plurality of two-dimensional displays 2 a 01, 2 a02, a total reflecting mirror 2 a 03 (e.g.,reflectivity/transmittivity=100/0) and a partial reflecting mirror 2 a04 (e.g., reflectivity/transmittivity=50/50) are used to construct anoptical system on which to place a plurality of two-dimensional imagesdescribed in the previous first and second embodiments.

[0231] By changing the arrangements of these constitutional components,it is possible to place an image plane 2 a 05 and an image plane 2 a 06at different positions in the direction of depth, the image plane 2 a 05being formed by reflecting the displayed image of the two-dimensionaldisplay 2 a 01 by the total reflecting mirror 2 a 03 and passing itthrough the partial reflecting mirror 2 a 04, the image plane 2 a 06being formed by reflecting the displayed image of the two-dimensionaldisplay 2 a 02 by the partial reflecting mirror 2 a 04.

[0232] This optical system uses only mirrors and thus has the advantageof less degradation of picture quality.

[0233] The two-dimensional displays 2 a 01, 2 a 02 may use CRT, liquidcrystal display, LED display, plasma display, FED display, DMD display,projection type display and line drawing type display.

[0234] It is obvious that the similar effect of this invention can beproduced even when the total reflecting mirror 2 a 03 of this embodimentis replaced with a partial reflecting mirror, although this lowers thebrightness of image of the two-dimensional display 2 a 01.

[0235] While this embodiment has described a case where the order ofdepth positions of image planes are equal to the order of depthpositions of the two-dimensional displays, it is apparent that the orderof depth positions of the image planes can be changed freely by changingthe distances from the total reflecting mirror or partial reflectingmirror to the respective two-dimensional displays.

[0236] [A-0023]

[0237] As shown in FIG. 17B, an optical system for arranging a pluralityof two-dimensional images described in the previous embodiments 1 and 2can be constructed by directly arranging the two-dimensional display 2 a01 without using the total reflecting mirror 2 a 03 and by using thepartial reflecting mirror 2 a 04 (e.g.,reflectivity/transmittivity=50/50).

[0238] That is, the image plane 2 a 05, which is formed by passing thedisplayed image of the two-dimensional display 2 a 01 through thepartial reflecting mirror 2 a 04, and the image plane 2 a 06, which isformed by reflecting the displayed image of the two-dimensional display2 a 02 by the partial reflecting mirror 2 a 04, can be located atdifferent positions in the direction of depth.

[0239] [A-0024]

[0240] While this embodiment has described a case where the order ofdepth positions of the image planes is equal to the order of the depthpositions of the two-dimensional displays, it is obvious that the orderof the depth positions of the image planes can be changed freely bychanging the distances from the partial reflecting mirror to therespective two-dimensional displays.

[0241] One example which can change the position of the image plane moreflexibly by incorporating lens or the like in the optical system isshown in FIGS. 18A and 18B.

[0242] As shown in FIG. 18A, by adding convex lenses 2 b 07, 2 b 08 tothe optical system, which comprises a plurality of two-dimensionaldisplays 2 b 01, 2 b 02, a total reflecting mirror 2 b 03 (e.g.,reflectivity/transmittivity=100/0) and a partial reflecting mirror 2 b04 (e.g., reflectivity/transmittivity=50/50), in order to change theimage position, it is seen that the positional relation between theimage plane 2 b 05 and the image plane 2 b 06, which has been restrictedby the size of the displays, can be more flexibly set.

[0243] It is obvious that the similar effect of this invention can beobtained even if the total reflecting mirror 2 b 03 of this embodimentis replaced with a partial reflecting mirror, although this lowers thebrightness of an image of the two-dimensional display 2 b 01.

[0244] While in this embodiment we have described a case where the orderof depth positions of image planes is equal to the order of depthpositions of two-dimensional displays, it is obvious that the order ofdepth positions of image planes can be changed freely by changing thedistances from the total reflecting mirror or partial reflecting mirrorto the two-dimensional displays or by installing lens or the like in theoptical system.

[0245] [A-0025]

[0246] Further, as shown in FIG. 8B, by adding convex lenses 2 b 07, 2 b08 to the optical system, which includes the two-dimensional display 2 b01 directly installed without using the total reflecting mirror 2 b 03and also a partial reflecting mirror 2 b 04 (e.g.,reflectivity/transmittivity=50/50), to change the image position, it isseen that the positional relation between the image plane 2 b 05 and theimage plane 2 b 06, which has been restricted by the size of thedisplays, can be more flexibly set.

[0247] As in the ordinary lens system, it may of course be advantageousin terms of distortion to use a combination lens in addition to convexlenses.

[0248] Further, although this embodiment has shown a case where virtualimages are used which are formed by installing the two-dimensionaldisplays at positions within a lens focal length, it is obvious that theinvention can also be applied to a case where real images are used whichare formed by installing the two-dimensional displays at positionsoutside the lens focal length.

[0249] While this embodiment has described a case where the order ofdepth positions of image planes is equal to the order of depth positionsof the two-dimensional displays, it is obvious that the order of depthpositions of image planes can be changed freely by changing thedistances from the partial reflecting mirror to the two-dimensionaldisplays or installing lens or the like in the optical system.

[0250] [A-0026]

[0251]FIG. 19 shows an example that uses an increased number oftwo-dimensional displays.

[0252] In this case, a plurality of two-dimensional displays 2 c 01, 2 c02, 2 c 03, 2 c 04, 2 c 05, a total reflecting mirror 2 c 06 (e.g.,reflectivity/transmittivity=100/0) and partial reflecting mirrors 2 c 07(e.g., reflectivity/transmittivity=50/50), 2 c 08 (e.g.,reflectivity/transmittivity=33.3/66.7), 2 c 09 (e.g.,reflectivity/transmittivity=25/75), 2 c 10 (e.g.,reflectivity/transmittivity=20/80) are used to construct an opticalsystem to arrange a plurality of two-dimensional images.

[0253] By changing the arrangements of these constitutional components,it is possible to place an image plane 2 c 11 and image planes 2 c 12-2c 15 at different positions in the direction of depth, the image plane 2c 11 being formed by reflecting the displayed image of thetwo-dimensional display 2 c 01 by the total reflecting mirror 2 c 06 andpassing it through the partial reflecting mirrors 2 c 07-2 c 10, theimage planes 2 c 12-2 c 15 being formed by reflecting the displayedimages of the two-dimensional displays 2 c 02-2 c 05 by the partialreflecting mirrors 2 c 07-2 c 10 and passing them through the partialreflecting mirrors.

[0254] This optical system uses only mirrors and thus has the advantageof less degradation of picture quality.

[0255] While this embodiment has described a case where there are fivetwo-dimensional displays, it is apparent that the similar configurationcan be adopted when a different number of two-dimensional displays areused.

[0256] In this case also, it is obvious that adding lens systems asshown in FIGS. 17 and 18 makes it easy to control the positions of imageplanes.

[0257] It is also obvious that replacing the total reflecting mirror 2 c03 in this embodiment with a partial reflecting mirror will produce thesimilar effect to that of the invention, although this lowers thebrightness of the image of the two-dimensional display 2 c 01.

[0258] While this embodiment has described a case where the order ofdepth positions of image planes are equal to the order of depthpositions of the two-dimensional displays, it is apparent that the orderof depth positions of the image planes can be changed freely by changingthe distances from the total reflecting mirror or partial reflectingmirror to the respective two-dimensional displays.

[0259] [A-0027]

[0260]FIG. 20 shows one example of an optical system for arranging aplurality of two-dimensional images which is constructed by using aplurality of projection type two-dimensional displays (for example, CRTtype, LCD type, ILV type and DMD type) 2 d 01, 2 d 02, 2 d 03, 2 d 04, 2d 05 and scatter plates 2 d 06, 2 d 07, 2 d 08, 2 d 09, 2 d 10 and byprojecting images from the projectors onto the scatter plates.

[0261] Here, the scatter plates 2 d 06-2 d 10 may be such devices as cancontrol scattering/transmission or reflection/transmission, such aspolymer dispersed liquid crystal devices, holographic polymer dispersedliquid crystal devices or combined devices of liquid crystal andmulti-lens array. Shutters 2 d 11-2 d 15 may be such devices as cancontrol transmission/interruption, such as twisted nematic liquidcrystal devices, ferroelectric liquid crystal devices or mechanicalshutter devices.

[0262] The scatter plates 2 d 06-2 d 10 are arranged at different depthpositions, the focusing planes of the projector type two-dimensionaldisplays 2 d 01-2 d 05 are aligned with these scatter plates 2 d 06-2 d10, images are projected onto the scatter plates, and thescattering/transmission timing of the scatter plates 2 d 06-2 d 10 issynchronized with the transmission/interruption timing of the shutters 2d 11-2 d 15 when activating the scatter plates and the shutters. Thisenables the depth positions of the image planes 2 d 11-2 d 15 formed onthe scatter plates 2 d 06-2 d 10 to be controlled on a time divisionbasis.

[0263] In this way, the use of projectors provides an advantage ofenhanced level of freedom of display layout.

[0264] [A-0028]

[0265] Although this embodiment has described a case where there arefive two-dimensional displays, the similar configuration can be employedwhen a different number of displays are provided.

[0266] It is obvious that the lamps of projectors can be turned on oroff instead of using the shutters.

[0267] Further, although the third embodiment mainly concerns a casewhere the image planes are located near, within or beyond thethree-dimensional display, these image planes can easily be located awayfrom or in front of the three-dimensional display. One such example isshown in FIG. 21.

[0268] For example, it can easily be seen that by arranging a lenssystem 3 e 03 in front of an optical system 3 e 01 as shown in FIG. 21,the internal image planes 3 e 02 can be moved to the positions ofexternal image planes 3 e 04.

[0269] This offers the advantage that because the images are reproducedfloating in space, the images are more likely to look three-dimensionalto the observer than when the images are located inside or behind thedisplay.

[0270] [A-0029]

[0271] [Embodiment 4]

[0272] The fourth embodiment of the present invention is an example inwhich the optical system in the previous embodiments 1, 2 for arranginga plurality of two-dimensional images is constructed by using avolumetric three-dimensional display.

[0273] As described in “Three-Dimensional Display” (by Senju Masuda,published by Sangyo Tosho K.K.), the volumetric three-dimensionaldisplay performs three-dimensional image presentation by stackingtwo-dimensional images (same as the two-dimensional images in theembodiment 1) sampled in the direction of depth.

[0274] The volumetric three-dimensional display includes a varifocalmirror type and a vibration screen type.

[0275] The varifocal mirror type, as shown in FIG. 22, transmits animage displayed on the two-dimensional 204 such as television through ahalf mirror 201 and a varifocal mirror 202 to form a three-dimensionalimage (virtual image) for an observer 100.

[0276] The varifocal mirror 202, a key device in this method, is made byapplying metal such as aluminum or multilayer dielectric on the surfaceof a woofer (low tone reproducing speaker) to form a concave mirror.When vibrated like an ordinary woofer, the concave mirror portionchanges its curvature to change the focal length.

[0277] Hence, the position of a virtual image or a real image of thetwo-dimensional display 204 can be changed by changing the focal length.

[0278] Therefore, by displaying images sampled in the direction of depth(two-dimensional images obtained by slicing a three-dimensional objectat positions shifted in the direction of depth and sampling the slicedportions) on the two-dimensional display 204 in synchronism with thechange in the focal length of the varifocal mirror 202, it is possibleto form a three-dimensional image on a time division basis (by takingadvantage of the after image effect).

[0279] With this method and apparatus, this invention can provide aplurality of two-dimensional images by repeating a short-durationactivation of the two-dimensional display a number of times.

[0280] The depth position of an image plane can be specified by thevibration position of the varifocal mirror 202.

[0281] Therefore, changing the brightness of the two-dimensional imagesdescribed in the preceding embodiments 1, 2 and displaying the images onthe image planes can produce the effect of this invention.

[0282] In addition to few moving parts, this method also has anadvantage of being able to form a plurality of image planes easily.

[0283] [A-0030]

[0284] The vibration screen type volumetric three-dimensional display,as shown in FIG. 23, includes: a vibration screen (e.g., diffusionplate, lenticular plate and fly's eye lens) 301 that vibrates in thedirection of depth; an optical system 302 including lens; a scanner forraster scanning a laser beam in horizontal and vertical directions(horizontal/vertical scanner comprising, for example, a light deflectorusing a polygon mirror and a galvanometer mirror) 303; and a laser lightsource 304.

[0285] This method drives the scanner 303 at high speed when thevibration screen 301 is at a desired depth position, writes a sampledimage corresponding to that depth position on the screen, and repeatsthis process by changing the depth position within the after image time,thereby reproducing a three-dimensional image.

[0286] With this method and apparatus, this embodiment can present aplurality of two-dimensional image planes by repeating within the afterimage time a process of writing the sample image on the vibration screen301 at high speed.

[0287] The depth position of the image plane can be specified by theposition of the vibration screen 301.

[0288] Hence, by changing the brightness of the two-dimensional imagesdescribed in the preceding embodiments 1, 2 and displaying the images onthese image planes, the effect of this invention can be produced.

[0289] This method has the advantages of being able to easily suppressdistortions on the screen surface and easily form a plurality of imageplanes.

[0290] [A-0031]

[0291] [Embodiment 5]

[0292] The fifth embodiment of the present invention is a rotary LEDtype three-dimensional display, which, as shown in FIG. 24, includes anLED display 401 having an LED array, a rotating device 402 for rotatingthe LED display 401, and a video supply device 403 for feeding a videosignal to the LED display 401.

[0293] This method requires sampling a three-dimensional object in polarcoordinates with the rotating axis of the LED display 401 as a center.

[0294] The two-dimensional image sampled in the polar coordinates isdisplayed on the LED display 401 in synchronism with the rotation of theLED display 401 and this process is repeated by changing the rotationangle to represent a three-dimensional image.

[0295] With this method and apparatus, this embodiment can present aplurality of two-dimensional image planes by converting a desiredtwo-dimensional image plane into the polar coordinates, displaying athigh speed an image on LEDs at the converted position coordinates withinthe after image time, and repeating this process while changing therotation angle.

[0296] Then, by changing the brightness of the two-dimensional imagesdescribed in the preceding embodiments 1, 2 and displaying the images onthese image planes, the effect of this invention can be produced.

[0297] This method offers the advantages of being able to easilysuppress distortions on the screen surface, rotate the LED display 401relatively easily, and easily form a plurality of image planes.

[0298] [A-0032]

[0299] [Embodiment 6]

[0300] The sixth embodiment of the present invention is a synthalyzertype three-dimensional display which, as shown in FIG. 25, includes afilm recorded with two-dimensional images or a two-dimensional display(e.g., CRT and liquid crystal display) 501, a conversion optical systemsuch as prism and mirror 502, and a projection drum 503. Denoted 504 isa light source and 505 a shutter.

[0301] The projection drum 503, a key device in this method, is made ofa transparent material (e.g., glass and acrylics or other transparentplastics) and has a varying thickness. The image of the film ortwo-dimensional display 501 is projected through the projection drum todisplay an image.

[0302] This method utilizes the fact that as the projection drum 503 isrotated, the drum thickness changes causing the position of the imageplane to change.

[0303] Thus, by displaying images sampled in the direction of depth(two-dimensional images obtained by slicing a three-dimensional objectat positions shifted in the direction of depth and sampling the slicedportions) on the two-dimensional display 501 in synchronism with thechange in the position of the image plane, it is possible to form athree-dimensional image on a time division basis (by utilizing the afterimage effect).

[0304] With this method and apparatus, this embodiment can present aplurality of two-dimensional image planes by repeating theshort-duration displaying of the film or two-dimensional display anumber of times within the after image time.

[0305] The depth position of the image plane can be specified by thethickness of the projection drum.

[0306] Therefore, by changing the brightness of the two-dimensionalimages described in the preceding embodiments 1, 2 and displaying theimages on these image planes, the effect of this invention can beobtained.

[0307] In addition to few moving parts, this method has the advantage ofbeing able to form a plurality of image planes easily.

[0308] The invention realized by the inventor has been described indetail in conjunction with embodiments. It should be noted that theinvention is not limited to these embodiments and that variousmodifications may be made without departing from the spirit of theinvention.

[0309] [A-0033]

[0310] The advantages and effects obtained by the representativeembodiments described above may be summarized briefly as follows.

[0311] [A-0034]

[0312] Because a plurality of two-dimensional images obtained by slicinga three-dimensional object at positions shifted in the direction ofdepth and sampling the sliced portions are displayed on planes 1−N (N≧2)having different depth positions from an observer and because thebrightness of each of the two-dimensional images on respective planes ischanged independently of each other, it is possible to suppresscontradictions among physiological factors of stereoscopy, reduce theamount of information, and reproduce an electrically rewritablethree-dimensional image.

[0313] [B-0019]

[0314] [Embodiment 7]

[0315]FIGS. 26A and 26B show a conceptual diagram showing the outlineconfiguration of a three-dimensional display according to thisembodiment. For components of the three-dimensional display of thisembodiment that are identical with the corresponding components of thepreceding embodiments 1 to 6, detailed explanations of theirconstructions and operations are omitted.

[0316] [B-0020]

[0317] In the three-dimensional display of this embodiment, as shown inFIG. 26A, a two-dimensional image with depth information which wasgenerated by a two-dimensional image generation device 1102 isdistributed into a plurality of images (in this case, five images) fordifferent depth positions by a distributor 1103. The brightness for eachof the distributed two-dimensional images with depth information ischanged by a brightness change device 1104 according to the depthposition of the image. The display elements are moved by a positionchange device (two-dimensional image change device) 1105 to suchpositions that the axes of the images as seen from an observer overlapeach other, and the brightness changed images are displayed on thetwo-dimensional displays 1106-1110, thus providing a three-dimensionalrepresentation.

[0318] [B-0021]

[0319]FIG. 27 is a conceptual diagram showing the working of thedistributor 1103. An image 1207 to be represented between an image plane1202 and an image plane 1203 is displayed on the image plane 1202 andthe image plane 1203. An image 1208 to be represented between imageplanes 1203 and 1204 is displayed on the image planes 1203 and 1204.Images to be represented between image planes 1204 and 1205 and betweenimage planes 1205 and 1206 are displayed in the similar way. The imageto be represented (for example, image 1207) may be located at anyposition between the image planes 1202 and 1203. For the image 1209 thatis to be represented straddling an image plane (for example, image plane1204), a part to be shown in front of the image plane 1204 is displayedin the same way as the front image 1208 and a part to be shown behindthe image plane 1204 is displayed in the same way as the rear image1210.

[0320] [B-0022]

[0321] In FIG. 26B, a two-dimensional image with depth information whichwas generated by a two-dimensional image generation device 1122 isdistributed into a plurality of images (in this case, five images) fordifferent depth positions by a distributor 1123. The brightness for eachof the distributed two-dimensional images with depth information ischanged by a brightness change device 1124 according to the depthposition of the image. Displays 1126-1130 are moved by a position changedevice (two-dimensional image change device) 1125 to such positions thatthe axes of the images as seen from an observer overlap each other, andthe brightness changed images are displayed on these displays 1126-1130thus providing a three-dimensional representation.

[0322] [B-0023]

[0323]FIGS. 28A to 28C are conceptual diagrams showing how an imagemoves, according to this embodiment.

[0324]FIG. 28A shows a conceptual diagram for a case where athree-dimensional image is reproduced at around an intermediate partbetween two image planes 1301 and 1302. When the observer views from aviewing position of an observer 1303, the images displayed on the frontand rear image planes are located at images 1306 and 1309. When theviewing position of the observer 1303 moves to a viewing position of anobserver 1304, the image 1306 is moved to a position of an image 1307and the image 1309 to a position of an image 1311 because thereproducing position of the three-dimensional image 312 must be fixed.When the viewing position moves to a viewing position of an observer1305, the images are moved to positions of images 1308 and 1310respectively.

[0325] [B-0024]

[0326]FIG. 28B is a conceptual diagram for a case where athree-dimensional image 1313 is reproduced between two image planes 1321and 1322 at a position close to the image plane 1322. When the observerviews from a viewing position of an observer 1323, the images displayedon the front and rear image planes are located at images 1326 and 1329.

[0327] [B-0025]

[0328] When the viewing point of the observer 1323 moves to a viewingposition of an observer 1324, the image 1326 is moved to a position ofan image 1327 and the image 1329 is left almost at its position becausethe reproducing position of the three-dimensional image 1313 needs to befixed. When the viewing point moves to a viewing position of an observer1325, the image 1326 is moved to a position of an image 1328.

[0329] [B-0026]

[0330]FIG. 28C is a conceptual diagram for a case where athree-dimensional image 1314 is reproduced between two image planes 1331and 1332 at a position close to the image plane 1331. When the observerviews from a viewing position of an observer 1333, the images displayedon the front and rear image planes are located at images 1336, 1337.

[0331] [B-0027]

[0332] When the viewing point of the observer 1333 moves to a viewingposition of an observer 1334, the image 1337 is moved to a position ofan image 1339 and the image 1336 is left almost at its position becausethe reproducing position of the three-dimensional image 1314 needs to befixed. Similarly, when the viewing point moves to a viewing position ofan observer 1335, the image 1337 is moved to a position of an image1338.

[0333] [B-0028]

[0334] By combining the image moving methods of FIGS. 28A to 28Caccording to the reproducing position of a three-dimensional image, itis possible to eliminate a double image caused by positional discrepancybetween the front and rear images even when the viewing point of anobserver changes and to ensure that the positions of gravity centers andoutlines of the images on the front and rear image planes snugly overlapso that the observer can recognize the display as a representation of asingle object.

[0335] [B-0029]

[0336]FIGS. 29A and 29B are conceptual diagrams showing how the displayelements are moved.

[0337] One method of moving an image is, as shown in FIGS. 29A and 29B,to move an image 1403 displayed on a two-dimensional display 401vertically or horizontally, or to enlarge or reduce an image 1413displayed on a two-dimensional display 411, or to combine these methodsand electrically rewrite the display element. In that case, when aFigure needs to be deformed slightly (as by trapezoidal deformation) aswhen an observer moves greatly, the display element on the display isalso changed at the same time. When the amount of movement of the imageis small, such a change is not necessary as long as the displayed objectlooks natural to the observer.

[0338] [B-0030]

[0339] As the observer moves, the displayed image is rewritten into animage as it will appear when viewed from the observer, thus producing amovement parallax, too. For example, when the observer moves to theleft, the displayed image is rewritten into an image as it will appearwhen viewed from the left viewing point corresponding to the position ofthe observer. By rewriting the image according to the change in positionof the observer, the required movement parallax can be realized. For thevertical movement of the observer also, the corresponding movementparallax is produced by the similar method.

[0340] [B-0031]

[0341] Another method of moving the image, as shown in FIGS. 30A, 30Band 31, is to mechanically move two-dimensional displays. The mechanicalmoving method includes: moving two-dimensional displays 1501, 1502, 1503(FIG. 30A); in a three-dimensional display having half mirrors, rotatingthe half mirrors 1514, 1515 (FIG. 30B); and moving an entirethree-dimensional display 1601 (FIG. 31).

[0342] [B-0032]

[0343] When it is necessary to cause a slight deformation to a Figure(as by trapezoidal deformation), the display element on the display isalso changed at the same time or corrections are made on an opticalsystem such as prism. The optical system for corrections may include oneof a prism, a lens and parallel plates, or a combination of these. Whenthe amount of movement of an image is small, such a change need not beperformed as long as the displayed object looks natural to the observer.Mechanically moving the displays changes physical positions of thedisplays and thus can expand a viewing zone. In the method of moving theentire three-dimensional display, the viewing zone can be expanded bymaking the movement follow the position of the observer.

[0344] [B-0033]

[0345] As a further image moving method, it is possible to combine thedisplay element moving method with the mechanical moving method. In thismethod, to follow a large movement of an observer, the image is moved bythe mechanical moving method to expand the viewing zone. To follow asmall movement of an observer, the display element is moved. Thiscombined method can simplify the moving apparatus, prevent the observerfrom feeling incongruous, and ensure swift movement of images.

[0346] [B-0034]

[0347] The movement of an observer may preferably be detected bydetermining the position of the observer relative to a three-dimensionaldisplay 701 by using an infrared sensor 1702 as shown in FIG. 32A, anultrasonic distance sensor or laser distance sensor 1703 as shown inFIG. 32B and an optical sensor as shown in FIG. 32C. For detecting theposition of a human using the above-described kinds of sensors, publiclyknown technologies may be used. Other known technologies may also beused, which include a method that detects the position of an observerfrom the image provided by a camera 1805 as shown in FIG. 33A and amethod that uses a magnetic sensor 1807 possessed by an observer or amagnetic sensor 1806 installed in the three-dimensional display todetect the position of an observer.

[0348] [B-0035]

[0349] The present invention has been described in detail in conjunctionwith embodiments and it should be noted, however, that the invention isnot limited to these embodiments and that various modifications may bemade without departing from the spirit of the invention.

[0350] [B-0036]

[0351] The advantages of this embodiment may be briefly summarized asfollows.

[0352] (1) When the viewing point of an observer changes or when theobserver moves, this embodiment can eliminate positional discrepanciesbetween the front and rear display images or minimize the discrepanciesto such an extent that the displayed object does not look unnatural,thus making it possible to reproduce a three-dimensional image with noor little blur, which would otherwise be caused by deviated overlappingof the front and rear images.

[0353] (2) When the viewing point of an observer changes or when theobserver moves, the two-dimensional images displayed on respectivedisplays are changed according to the movement of the observer's viewingpoint. This can expand the viewing zone.

[0354] (3), When the viewing point of an observer changes or when theobserver moves, the displays or the three-dimensional display are movedaccording to the movement of the observer's viewing point. This canexpand the viewing zone.

[0355] [C-0013]

[0356] [Embodiment 8]

[0357]FIG. 34 is a block diagram showing a concept of athree-dimensional display according to this invention.

[0358] The three-dimensional representation method of this embodiment,too, has a plurality of image planes (display surfaces), for exampleimage planes 2102, 2103, set in front of an observer 2101, as shown inFIG. 34, and a plurality of two-dimensional images are displayed onthese image planes by using two-dimensional displays and an opticalsystem.

[0359] A three-dimensional object to be presented to the observer 2101is projected onto the image planes 2102, 2103 along the line of sight ofboth eyes of the observer to generate two-dimensional images.

[0360] The two-dimensional images can be generated by a variety ofmethods, which include one that uses two-dimensional images of theobject shot by camera from the line of sight, one that synthesizes aplurality of two-dimensional images shot from different directions, andone that uses a synthesizing technique or modeling technique based oncomputer graphics.

[0361] [C-0014]

[0362] With this embodiment, when an object to be presented is aplurality of objects located at different depth positions andoverlapping each other on the line of sight of the observer 2101, animage generator 2105 generates for each of the objects to be presentedtwo-dimensional images that are to be displayed simultaneously on aplurality of image planes, e.g., the image planes 2102, 2103.

[0363] That is, in this embodiment, for each object to be displayedthere are generated two-dimensional images which are projected from theobject onto the image planes 2102, 2103 from the line of sight of botheyes of the observer 2101.

[0364] [C-0015]

[0365] In this case, two-dimensional images to be displayed at desireddepth positions (two-dimensional images for each of the objects to bepresented) are generated by the image generator 2105 shown in FIG. 34 inthe order from the near depth position to the far depth position withrespect to the observer, in the reverse order or in a random order.

[0366] Then, the brightness of the generated two-dimensional images tobe displayed on the image planes 2102, 2103 is changed by a brightnesschange device 2104 to the brightness values corresponding to their depthpositions, and the two-dimensional images thus generated are displayedon the image planes 2102, 2103.

[0367] [C-0016]

[0368] A synchronizer 2106 synchronizes the depth positions for whichthe image generator 2105 generates the images with the depth positionsfor which the synchronizer 2106 changes the brightness of the images.That is, the images and their corresponding depth positions aresynchronized.

[0369] The synchronizer 2106 shown in FIG. 34 is conceptuallyillustrated, and the brightness can be changed either mechanically or bysoftware. Two or more synchronizers 2106 may be used.

[0370] Further, the brightness change device 21C4 and the synchronizer2106 may be constructed as one device. [C-0017]

[0371] A method of displaying a three-dimensional image on thethree-dimensional display according to this embodiment will be describedby referring to FIG. 35.

[0372] Step 2000: Two-dimensional images of an object that one wantsreproduced at a front position as viewed from an observer, such as athree-dimensional image 2204, are changed in brightness by thebrightness change device 2104 and the synchronizer 2106 and thendisplayed on image planes 2202, 2203 to reproduce the three-dimensionalimage 2204.

[0373] Step 2001: Next, two-dimensional images of an object that onewants reproduced at an intermediate position as viewed from an observer,such as a three-dimensional image 2214, are changed in brightness anddisplayed on image planes 2212, 2213 to reproduce the three-dimensionalimage 2214.

[0374] Step 2003: Next, two-dimensional images of an object that onewants reproduced at a rear position as viewed from an observer, such asa three-dimensional image 2224, are changed in brightness and displayedon image planes 2222, 2223 to reproduce the three-dimensional image2224.

[0375] Changing the brightness can be achieved by two methods: one is tochange the brightness according to the three-dimensional image to bedisplayed and then display the image, and one is to change thebrightness continuously while displaying the three-dimensional image.

[0376] For example, the brightness of the front image plane may bechanged from high to middle to low and the brightness of the rear imageplane from low to middle to high so that the overall brightness as seenby the observer remains constant in order to change the position atwhich the three-dimensional image is reproduced from the front towardthe rear. It is possible to reverse the brightness changing order.Another method is to change the brightness freely according to anydesired position where a three-dimensional image is to be reproduced.

[0377] [C-0018]

[0378] This embodiment greatly differs from conventional techniques inthat the steps 2000, 2001 and 2002 in FIG. 35 are repeated at high speedduring the display of image.

[0379] Repeating the steps 2000, 2001 and 2002 of FIG. 35 at high speedallows the observer 2231 to see the three-dimensional images 2234, 2235,2236 reproduced at respective positions as shown in the state 2003 andalso to see the rear image through the front image. Here, 2232 and 2233denote image planes and 2234, 2235 and 2236 represent three-dimensionalimages reproduced.

[0380] The speed at which the steps 2000, 2001 and 2002 of FIG. 5 arerepeated is set within the after image time of human eye, for example at60 Hz or higher, to realize displaying of a three-dimensional imagewithout flicker.

[0381] That is, displaying two or more overlapping three-dimensionalimages can be achieved by performing the image displaying procedures ona time division basis at high speed such that the resultant images areall displayed sequentially within the after image time of human eye.

[0382] The number of brightness-changed two-dimensional images fordifferent depth positions needs to be greater than the maximum number ofbrightness-changed images required to display the overlapping portionsof the three-dimensional images.

[0383] [C-0019]

[0384]FIG. 36 is a schematic diagram showing the outline configurationof a three-dimensional display according to an eighth embodiment of theinvention.

[0385] In the three-dimensional display of this embodiment,two-dimensional displays 2304, 2305 define the front and rear imageplanes respectively and the two-dimensional images displayed on the twoimage planes are arranged on the same optical axis by half mirrors 2302,2303.

[0386] The images displayed on the two-dimensional displays 2304, 2305are, as shown in FIG. 35, rapidly changed in brightness and displayed tothe observer 2301 repetitively.

[0387] The two-dimensional displays 2304, 2305 may use CRT, liquidcrystal display and plasma display and, when higher speed is required,can use displays using ferroelectric liquid crystals orantiferroelectric liquid crystals.

[0388] Alternatively, it is possible to use a display that allowshigh-speed random access to individual pixels, such as a display ofoscilloscope.

[0389] In this case, the brightness levels of two-dimensional imagesdisplayed on the two-dimensional displays 2304, 2305 are changed by thetwo-dimensional displays 2304, 2305 themselves.

[0390] [C-0021]

[0391] [Embodiment 9]

[0392]FIG. 37 is a schematic diagram showing the outline configurationof a three-dimensional display according to a ninth embodiment of thepresent invention. Reference number 2401 represents an observer, 2402and 2403 half mirrors, and 2404 and 2405 two-dimensional displays.

[0393] The three-dimensional display of this embodiment differs from thethree-dimensional display of the eighth embodiment in that thebrightness of displayed images are changed by beam attenuating filters2406, 2407.

[0394] The beam attenuating filters 2406, 2407 according to thisembodiment may be a filter that continuously changes its light intensityattenuation by mechanical rotation, a filter that electricallyattenuates light intensity by liquid crystals, a device that has slitshaving changing opening areas and arranged in the direction of rotationand which mechanically rotates the slits to change the brightness, and adevice which changes the opening time by a ferroelectric shutter tochange the brightness.

[0395] In the three-dimensional display of this embodiment, theattenuation of the beam attenuating filters 2406, 2407 is synchronizedwith the two-dimensional images displayed on the two-dimensionaldisplays 2404, 2405 to display a three-dimensional image.

[0396] [C-0022]

[0397] [Embodiment 10]

[0398]FIG. 38 is a schematic diagram showing the outline configurationof a three-dimensional display according to a tenth embodiment of theinvention. Reference number 2501 represents an observer, 2502 and 2503half mirrors, 2504 and 2505 screens, 2506-2511 two-dimensional displays,and 2512-2517 shutters.

[0399] In the three-dimensional display of this embodiment a pluralityof projector type two-dimensional displays 2506-2511 are used.

[0400] For example, a two-dimensional display 2506 displays atwo-dimensional image for a front three-dimensional image as viewed froman observer, a two-dimensional display 2507 displays a two-dimensionalimage for an intermediate three-dimensional image, and a two-dimensionaldisplay 2508 displays a two-dimensional image for a rearthree-dimensional image. Shutters 2512-2514 are operated to projectthese two-dimensional images sequentially on a time division basis ontoa screen 2504.

[0401] Similarly, a two-dimensional display 2509 displays atwo-dimensional image for a front three-dimensional image as viewed froman observer, a two-dimensional display 2510 displays a two-dimensionalimage for an intermediate three-dimensional image, and a two-dimensionaldisplay 2511 displays a two-dimensional image for a rearthree-dimensional image. Shutters 2515-2517 are operated to projectthese two-dimensional images sequentially on a time division basis ontoa screen 2505.

[0402] Then, the two-dimensional images displayed on the screens 2504,2505 are arranged on the same optical axis by half mirrors 2502, 2053.

[0403] In this embodiment, the brightness of each of the two-dimensionalimages projected from the two-dimensional displays 2506-2511 is presetto a desired brightness level corresponding to the depth position of thetwo-dimensional image displayed.

[0404] [C-0023]

[0405] [Embodiment 11]

[0406]FIG. 39 is a schematic diagram showing the outline configurationof a three-dimensional display according to a eleventh embodiment of theinvention. Reference number 2601 represents an observer, 2602 and 2603half mirrors, 2604 and 2605 screens, 2606-2611 two-dimensional displays,2612-1617 shutters, and 2618-2623 beam attenuating filters.

[0407] The three-dimensional display of this embodiment differs from thethree-dimensional display of the preceding tenth embodiment in that thebrightness of each of the two-dimensional images displayed on thetwo-dimensional displays 2606-2611 is changed by beam attenuatingfilters 2618-2623 installed at the front of the two-dimensional displays2606-2611.

[0408] For example, when three three-dimensional images are reproducedat positions shifted in the direction of depth by using thetwo-dimensional displays 2606-2608 that display two-dimensional imageson the front image plane and the two-dimensional displays 2609-2611 thatdisplay two-dimensional images on the rear image plane, the brightnessof each two-dimensional display can be set constant and therefore thebeam attenuating filters 2618-2623 may have fixed levels of attenuation.

[0409] [C-0024]

[0410] When three or more three-dimensional images are reproduced atpositions shifted in the direction of depth, the beam attenuatingfilters 2618-2623 may be a filter that continuously changes its lightintensity attenuation by mechanical rotation, a filter that electricallyattenuates light intensity by liquid crystals, a device that has slitshaving changing opening areas and arranged in the direction of rotationand which mechanically rotates the slits to change the brightness, and adevice which changes the opening time by a ferroelectric shutter tochange the brightness.

[0411] The attenuation of the beam attenuating filters 2618-2623 issynchronized with the two-dimensional images projected from thetwo-dimensional displays 2606-2611 to produce three-dimensional images.

[0412] [C-0025]

[0413] [Embodiment 12]

[0414]FIG. 40 is a schematic diagram showing the outline configurationof a three-dimensional display according to a twelfth embodiment of thepresent invention. Reference numeral 2701 denotes an observer, 2702-2707half mirrors, 2708-2713 two-dimensional displays, and 2714-2719shutters.

[0415] In the three-dimensional display of this embodiment, the lightaxes of the two-dimensional displays 2708-2710 are aligned with eachother by the half mirrors 2704, 2705, and the two-dimensional imagesdisplayed on the two-dimensional displays 2708-2710 are projected ontothe front image plane by the shutters 2714-2716 on a time divisionbasis. The light axes of the two-dimensional displays 2711-2713 arealigned with each other by the half mirrors 2706, 2707, and thetwo-dimensional images displayed on the two-dimensional displays2711-2713 are projected onto the rear image plane by the shutters2717-2719 on a time division basis.

[0416] [C-0026]

[0417] For the two-dimensional displays 2708-2713, a CRT, a liquidcrystal display and a plasma display may be used. When a faster speed isrequired, a display using ferroelectric liquid crystals orantiferroelectric liquid crystals may be used.

[0418] [C-0027]

[0419] Alternatively, it is possible to use a display that allowshigh-speed random access to individual pixels, such as a display ofoscilloscope.

[0420] In this case, the brightness levels of two-dimensional imagesdisplayed on the two-dimensional displays 2708-2713 are changed by thetwo-dimensional displays 2708-2713 themselves.

[0421] [C-0028]

[0422] [Embodiment 13]

[0423]FIG. 41 is a schematic diagram showing the outline configurationof a three-dimensional display according to a thirteenth embodiment ofthe invention. Reference number 2801 denotes an observer, 2802-2807 halfmirrors, 2808-2813 two-dimensional displays, 2714-2719 shutters and2720-2725 beam attenuating filters.

[0424] The three-dimensional display of this embodiment differs from thethree-dimensional display of the preceding twelfth embodiment in thatthe brightness of each of the two-dimensional images displayed on thetwo-dimensional displays 2808-2813 is changed by the beam attenuatingfilters 2720-2725 disposed at the front of the two-dimensional displays2808-2813.

[0425] For example, when three three-dimensional images are reproducedat positions shifted in the direction of depth by using thetwo-dimensional displays 2808-2810 that display two-dimensional imageson a front image plane and the two-dimensional displays 2811-2813 thatdisplay two-dimensional images on a rear image plane, the brightness ofeach two-dimensional display can be set constant and therefore the beamattenuating filters 2720-2725 can use fixed levels of attenuation.

[0426] [C-0029]

[0427] When three or more three-dimensional images are reproduced atpositions shifted in the direction of depth, the beam attenuatingfilters 2720-2725 may be a filter that continuously changes its lightintensity attenuation by mechanical rotation, a filter that electricallyattenuates light intensity by liquid crystals, a device that has slitshaving changing opening areas and arranged in the direction of rotationand which mechanically rotates the slits to change the brightness, and adevice which changes the opening time by a ferroelectric shutter tochange the brightness.

[0428] The attenuation of the beam attenuating filters 2720-2725 issynchronized with the two-dimensional images projected from thetwo-dimensional displays 2808-2813 to produce three-dimensional images.

[0429] [C-0030]

[0430] The invention has been described in detail in conjunction withembodiments. It should be noted, however, that the invention is notlimited to the embodiments but various modifications may be made withoutdeparting from the spirit of the invention.

[0431] [C-0031]

[0432] The advantages and effects produced by the representativeembodiments described in this specification may be summarized briefly asfollows.

[0433] [C-0032]

[0434] With this invention, a plurality of objects which have differentdepth positions and overlap each other on the line of sight of anobserver can be represented by three-dimensional images in such a waythat all the three-dimensional images can be seen by the observerwithout being hidden by the front images.

[0435] [D-0020]

[0436] [Embodiment 14]

[0437] The three-dimensional display according to a fourteenthembodiment of the present invention represent the overall depth positionof the entire three-dimensional object between a plurality of imagefocusing planes.

[0438]FIG. 42 shows the outline configuration of the three-dimensionaldisplay of the fourteenth embodiment of the invention. Thisthree-dimensional display includes a two-dimensional display 3100, apolarization varying device 3101 and a polarization type bifocal opticalsystem 3102.

[0439] The display light of a two-dimensional image displayed on thetwo-dimensional display 3100 is split and displayed onto two imagefocusing planes (in FIG. 42, image focusing planes 3103 and 3104) of thepolarization type bifocal optical system 3102 at a brightness ratio thatdepends on a polarization direction of exit light from the polarizationvarying device 3101.

[0440] When the polarization direction of exit light agrees with one ofintrinsic polarization directions (meaning two independent polarizationdirections) P11 of the polarization type bifocal optical system 3102,the two-dimensional image displayed on the two-dimensional display 3100is focused on, for example, the image focusing plane 3103. When thepolarization direction of the exit light matches the other intrinsicpolarization direction P12, the two-dimensional image displayed on thetwo-dimensional display 3100 is focused on the image focusing plane3104.

[0441] When the polarization direction is other than these two intrinsicpolarization directions (including linear polarization, circularpolarization, elliptical polarization, etc.), the brightness levels ofthe image focusing planes 3103 and 3104 are set according to a ratio ofcomponents of the exit light polarization direction as projected ontothe orthogonal intrinsic polarization directions.

[0442] [D-0021]

[0443] Among the two-dimensional displays 3100 are a CRT display, aliquid crystal display, an LED display, a plasma display, an FEDdisplay, a projection type display and a line drawing type display.

[0444] An example of the polarization varying device 3101 includes adevice using liquid crystals and a device using PLZT which hasbirefringence and can control the birefringence by an electric field.These devices will be described later.

[0445] Further, an example of the polarization type bifocal opticalsystem 3102 includes a device using liquid crystals and a device whichhas two optical systems with image focusing planes different from thoseof the polarization beam splitter or two optical systems with imagefocusing planes different from those of the beam splitter and thepolarizer. These devices will be described later.

[0446] [D-0022]

[0447] The basic operation of the three-dimensional display of thisembodiment will be explained.

[0448] In the three-dimensional display of this embodiment, as shown inFIG. 43, a three-dimensional object 3106 to be presented to an observer3105 is projected along the line of sight of both eyes of the observer3105 onto image focusing planes 3103, 3104 to form two-dimensionalimages 3107, which are then displayed on the two-dimensional displays3100 shown in FIG. 42.

[0449] The two-dimensional images 3107 may be generated in a variety ofways, which include a method that uses two-dimensional images of thethree-dimensional object 3106 shot by camera from the direction of lineof sight; a method that synthesizes a plurality of two-dimensionalimages shot from different directions; or a method that usessynthesizing and modeling techniques based on computer graphics.

[0450] [D-0023]

[0451] Each polarization varying element of the polarization varyingdevice 3101 is related to one or more groups of pixels on thetwo-dimensional display 3100.

[0452] For example, as shown in FIG. 44, one pixel 3110 of thetwo-dimensional display 3100 is related to one polarization varyingelement 3111 of the polarization varying device 3101. Or, as shown inFIG. 45, a plurality of pixels 120 of the two-dimensional display 3100are related to one polarization varying element 3121 of the polarizationvarying device 3101.

[0453] [D-0024]

[0454] Next, the exit light polarization direction of the polarizationvarying element (for example, 3111 of FIG. 44 or 3121 of FIG. 45) of thepolarization varying device 3101 is changed according to the depthposition of that part of the three-dimensional object 3106 whichcorresponds to the associated pixel (e.g., 3110 in FIG. 44) or pixels(e.g., 3120 in FIG. 45) of the two-dimensional display 3100.

[0455] This causes two-dimensional images with brightness levelscorresponding to the exit light polarization direction to be displayedon the image focusing planes 3103 and 3104.

[0456] The positional relation of the image focusing planes 3103, 3104is adjusted in advance by using an appropriate optical system so thatthe images on the image focusing planes 3103, 3104 overlap each other onthe line of sight of the observer 3105.

[0457] Overlapping the images of the image focusing planes 3103, 3104 onthe line of sight of the observer 3105 can be realized by putting thecenters or gravity centers of the two-dimensional images 3107 on theline of sight.

[0458] [D-0025]

[0459] The essential point of the three-dimensional display of thisembodiment is that, by changing the exit light polarization direction ofeach polarization varying element of the polarization varying device3101, the brightness of each part of the images on the image focusingplanes 3103, 3104 is changed according to the depth position of thethree-dimensional object 3106 while keeping constant the overallbrightness as seen by the observer 3105.

[0460] One example method of changing the brightness is explained belowby referring to FIGS. 46 to 49.

[0461] It is assumed that the image focusing plane 3103 is locatedcloser to the observer 3105 than the image focusing plane 3104 and thatthe intrinsic polarization directions of the polarization type bifocaloptical system 3102 for the image focusing planes 3103, 3104 are takenas p11 and p12.

[0462] As shown in FIG. 46, when the exit light polarization directionof each polarization varying element of the polarization varying device3101 coincides with p11, the brightness of the image on the imagefocusing plane 3103 becomes equal to the brightness of thethree-dimensional object 3106 and the brightness of the image on theimage focusing plane 3104 becomes zero, thus representing thethree-dimensional object 3106 positioned on the image focusing plane3103.

[0463] Next, as shown in FIG. 47, as the exit light polarizationdirection of each polarization varying element of the polarizationvarying device 3101 is tilted from p11, the brightness of the image onthe image focusing plane 3103 slightly lowers from that of FIG. 46 andthe brightness of the image on the image focusing plane 3104 increases,thus representing the three-dimensional object 3106 that has movedslightly away from the image focusing plane 3103 toward the imagefocusing plane 3104.

[0464] [D-0026]

[0465] Further, as shown in FIG. 48, when the exit light polarizationdirection of each polarization varying element of the polarizationvarying device 3101 is further tilted from that shown in FIG. 47, thebrightness of the image on the image focusing plane 3103 furtherdecreases from that of FIG. 47 and the brightness of the image on theimage focusing plane 3104 further increases, thus representing asituation where the three-dimensional object 3106 has moved further awayfrom the image focusing plane 3103 toward the image focusing plane 3104.

[0466] Finally, as shown in FIG. 49, when the exit light polarizationdirection of each polarization varying element of the polarizationvarying device 3101 coincides with p12, the brightness of the image onthe image focusing plane 3104 becomes equal to the brightness of thethree-dimensional object 3106 and the brightness of the image on theimage focusing plane 3103 becomes zero, thus representing a situationwhere the three-dimensional object 3106 is on the image focusing plane3104.

[0467] [D-0027]

[0468] With the above representation method, the observer 3105 perceivesthe three-dimensional object 3106 to be located between the imagefocusing planes 3103 and 3104 because of observer's physiological ormental factors or optical illusion although the images are actuallydisplayed on the image focusing planes 3103, 3104.

[0469] Because, unlike the conventional three-dimensional display, thethree-dimensional display of this embodiment has at least two imagedisplaying planes on the near and far sides of the optical illusionposition, it is possible to suppress contradictions among the binocularparallax, convergence and focusing—the problem experienced with theconventional three-dimensional display—which in turn is expected toreduce eyestrains.

[0470] Further, because, unlike the conventional three-dimensionaldisplay, the three-dimensional object even at an intermediate positionbetween the image planes appears three-dimensional to the observer, thisembodiment has the advantage of being able to provide a realisticthree-dimensional image representation, not the kind of conventionalsolidity presented by gathering sheet-divided depths.

[0471] The three-dimensional display of this embodiment also has theadvantage of being able to significantly reduce the amount of datarequired for three-dimensional representation because it can representeven a three-dimensional object disposed between a plurality of planes.

[0472] [D-0028]

[0473] Because the three-dimensional display of this embodiment utilizeshuman physiological or mental factors or optical illusion based onchanges in image brightness, there is an advantage that a coherent lightsource such as a laser is not required and that a color stereoscopicimage representation can be easily realized.

[0474] Further, because the three-dimensional display of this embodimentdoes not include mechanical driving parts, it has the advantage of lightweight and improved reliability.

[0475] Further, because the two-dimensional representation is achievedby the two-dimensional display 3100 and the depthwise representation isachieved by the polarization varying device 3101, this embodiment hasthe advantage of simple control.

[0476] Further, because the resolutions of images can be differentiated,the amount of information can be reduced. That is, in view of the factthat the resolution requirement for the depth direction is lower thanthat for the two-dimensional direction, it may be an effective method toreduce the resolution in the depth direction.

[0477] [D-0029]

[0478] In the three-dimensional display of this embodiment, the size ofthe device is not restricted by the position, interval and size of theimage focusing planes.

[0479] That is, it is possible to locate the image focusing planes 3103,3104 at the front side of the three-dimensional display as virtualplanes by an optical system, or at the rear side by another opticalsystem.

[0480] The image focusing planes 3103, 3104 can be spaced apart agreater distance than in this embodiment by an optical system.

[0481] Further, the size of the formed images can also be made largerthan in this embodiment by an optical system.

[0482] Thus, compared with a method in which displays are actuallyarranged, this embodiment has the advantage of being able to reduce theoverall size of the three-dimensional display.

[0483] [D-0030]

[0484] The above description concerns a case where the brightness levelsof the two-dimensional images 3107 on a plurality of image focusingplanes 3103, 3104 are changed while keeping constant the overallbrightness as seen by the observer. It is a common technique employed incomputer graphics to progressively reduce the overall brightness as seenby the observer 3105 toward the far side in order to make the image looksolid. It is obvious that the use of this technique also in thisembodiment can further enhance the three-dimensional effect.

[0485] Sequentially changing the two-dimensional images 3107 and thepolarization direction of the display light of the two-dimensionalimages 3107 and throwing it onto a plurality of image focusing planes3103, 3104 at different depth positions can generate a three-dimensionalvideo image.

[0486] While this embodiment has described a case where thethree-dimensional object 3106 to be represented is displayed astwo-dimensional images on two image focusing planes 3103, 3104, it isapparent that the similar effects can be expected if more than two imagefocusing planes are used.

[0487] This embodiment has described only the basic configuration and itis apparent that aberration can be reduced by adding optical systems.

[0488] Further, this embodiment has described a case where an observer3105 is located at the front center of the three-dimensional display. Ifthe observer 310 is located at other positions, it is apparent that thesimilar effects can easily be produced by changing or adding opticalsystems.

[0489] [D-0031]

[0490] [Embodiment 15]

[0491] The three-dimensional display according to a fifteenth embodimentof the invention differs from the preceding embodiment in that thethree-dimensional display represents the depth of the three-dimensionalobject itself.

[0492]FIG. 50 shows the outline configuration of the three-dimensionaldisplay of the fifteenth embodiment of the invention. Thethree-dimensional display, as with the fourteenth embodiment, includes atwo-dimensional display 3200, a polarization varying device 3201 and apolarization type bifocal optical system 3202.

[0493] In the three-dimensional display of this embodiment, too, thedisplay light of a two-dimensional image displayed on thetwo-dimensional display 3200 is split and displayed onto two imagefocusing planes (in FIG. 50, image focusing planes 3203 and 3204) of thepolarization type bifocal optical system 3202 at a brightness ratio thatdepends on a polarization direction of exit light from the polarizationvarying device 3201.

[0494] [D-0032]

[0495] The basic operation of the three-dimensional display of thisembodiment will be explained as follows.

[0496] First, the two-dimensional images 3207 of a three-dimensionalobject to be represented are displayed on the two-dimensional display3200.

[0497] Then, as shown in FIGS. 44 and 45, each polarization varyingelement of the polarization varying device 3201 is related to one ormore pixels of the two-dimensional display 3200.

[0498] Next, the exit light polarization direction of the relatedpolarization varying element is changed according to the depth positionof that part of the three-dimensional object which corresponds to theassociated pixel (e.g., 3110 in FIG. 44) or pixels (e.g., 3120 in FIG.45) of the two-dimensional display 3200.

[0499] This causes two-dimensional images with brightness levelscorresponding to the exit light polarization direction to be displayedon the image focusing planes 3203 and 3204.

[0500] The positional relation of the image focusing planes 3203, 3204is adjusted in advance by using an appropriate optical system so thatthe images on the image focusing planes 3203, 3204 overlap each other onthe line of sight of the observer 3205.

[0501] [D-0033]

[0502] The essential point of the three-dimensional display of thisembodiment is that, by changing the exit light polarization direction ofeach polarization varying element of the polarization varying device3201, the brightness of each part of the images on the image focusingplanes 3203, 3204 is changed according to the depth position of eachpart of the three-dimensional object while keeping constant the overallbrightness as seen by the observer 3205.

[0503] One example method of changing the brightness is explained belowby referring to FIGS. 51A and 51B.

[0504]FIG. 51A show an example image formed on an image focusing planeclose to the observer, for example image focusing plane 3203, and FIG.51B represents an example image formed on an image focusing plane remotefrom the observer, for example image focusing plane 3204.

[0505] When a cake, as shown in FIGS. 51A and 51B, is taken as anexample object, the top and bottom surfaces of the cake is almost flatexcept for candles stuck on the top, the wall surface is cylindrical,and the candles are arranged near the circumference of the top surfaceof the cake.

[0506] As shown in FIGS. 51A and 51B, in the two-dimensional images3207, on the top and bottom surfaces the upper parts represent theremote parts of the cake. On the wall surface, the central part of thewall surface corresponds to the near side of the cake, and as you gofrom the center toward the left and right, the surface position movestoward the far side. And the central part of the hidden wall surface,which is shown higher than the front wall surface, is located on the farside.

[0507] In this case, polarization direction of each part needs to bechanged by considering the two intrinsic polarization directions of thepolarization type bifocal optical system 3202 so that the brightnesslevels of the image focusing planes 3203, 3204 will change as follows.

[0508] [D-0034]

[0509] First, the brightness on the top and bottom surfaces isprogressively changed according to the depth position so that, as shownin FIG. 51A, on an image focusing plane 3203 close to the observer 3205a portion close to the observer 3205 (a lower part of thetwo-dimensional image 3207) has a higher brightness level and a portionremote from the observer (an upper part of the two-dimensional image3207) has a lower brightness level.

[0510] Further, on an image focusing plane 3204 remote from the observer3205, the brightness is progressively changed according to the depthposition so that, as shown in FIG. 51B, a portion close to the observer3205 (a lower part of the two-dimensional image 3207) has a lowerbrightness level and a portion remote from the observer (an upper partof the two-dimensional image 3207) has a higher brightness level.

[0511] Next, the brightness of the cylindrical portion is also changedprogressively according to its depth position so that, on an imagefocusing plane close to the observer 3205, a portion close to theobserver 3205 (around the center) has a higher brightness level and aportion remote from the observer (near the left and right end) has alower brightness level, as shown in FIG. 51A.

[0512] On an image focusing plane 3204 remote from the observer 3205,the brightness is changed progressively so that, as shown in FIG. 51B, aportion close to the observer 3205 (around the center) has a lowerbrightness level and a portion remote from the observer (near the leftand right end) has a higher brightness level.

[0513] In FIGS. 51A and 51B, the darker the image is shaded, the higherthe brightness level it represents.

[0514] With the above representation method, the observer 3205 perceivesas if there is a cylindrical cake with almost flat top and bottomsurfaces because of observer's physiological or mental factors oroptical illusion although what is actually shown to the observer istwo-dimensional images.

[0515] With this three-dimensional display of this embodiment, it ispossible to easily represent a three-dimensional object having acontinuous depth.

[0516] [D-0035]

[0517] [Embodiment 16]

[0518] A polarization type bifocal optical system that can be used inthe three-dimensional displays of the preceding embodiments will beexplained.

[0519]FIG. 52 shows examples of the polarization type bifocal opticalsystem that can be used in the three-dimensional displays of thepreceding embodiments.

[0520] The polarization type bifocal optical systems represented byreference numerals 3310-3313 in FIG. 52 each have a fixed focus lens3301 and a birefringent area 3302.

[0521] The fixed focus lens 3301 is formed by, for example, a convexlens of glass or plastics as shown in a polarization type bifocaloptical system 3313; a concave lens of glass or plastics as shown in apolarization type bifocal optical system 3312; or a lens systemcombining convex lens, concave lens and prism of glass or plastics or amirror system combining convex lens, concave lens and prism as shown inpolarization type bifocal optical systems 3310, 3311, respectively.

[0522] The birefringent area 3302 is formed of, for example, a medium ofliquid crystals or PLZT that has birefringence.

[0523] [D-0036]

[0524] Here, it is assumed that the refractive index of the fixed focuslens 3301 is n1, that the intrinsic polarization directions in thebirefringent area 3302 are p21 and p22, and that the refractive indicesin these polarization directions are n21 and n22.

[0525] When, for example, light enters from the birefringent area 3302,the incident light is split into polarized light beams havingpolarization directions of p21 and p22 according to the polarized state.The polarized beams propagate according to the refractive indices n21,n22 they sense, and contact the fixed focus lens 3301 of the refractiveindex of n1.

[0526] As shown in FIG. 53, the two polarized light beams, which remainsplit as they go out, form images at different positions according tothe difference in the refractive index. That is, this optical systemworks as a bifocal optical system that splits light beam according tothe polarization directions.

[0527] Conversely, when light enters from the fixed focus lens 3301side, the light is split according to the refractive indices associatedwith the intrinsic polarization directions and forms images on twodifferent image focusing planes.

[0528] [D-0037]

[0529] As shown in FIG. 52, when the birefringent area 3302 is liquidcrystals, the addition of an alignment layer 3303 can ensure uniformin-plane splitting of light entering from the birefringent area 3302side.

[0530] Even when the alignment layer 3303 is provided on only one of thebirefringent areas 3302, the incident light becomes twisted by its ownoptical activity according to the alignment of the birefringent medium.Because the refractive indices that the split light beams sense do notchange, the aforementioned effect will also be produced without problem.

[0531] Providing an alignment layer also on the side of an interfacewith the fixed focus lens 3301 is effective when light is thrown in fromthe fixed focus lens 3301 side or when such alignment-dependent opticalsystems are connected in series.

[0532] [D-0038]

[0533] In the polarization type bifocal optical systems shown in FIGS.52 and 53, even when the fixed focus lens 3301 is not provided, it isobvious that if one or both sides of the birefringent area 3302 areformed in a lens or prism shape as shown in FIG. 54, the effects similarto those shown in FIGS. 52 and 53 can be produced.

[0534] Liquid crystal are useful as a birefringent medium because oftheir large refractive anisotropy. Applicable kinds of liquid crystalsinclude ordinary nematic liquid crystal, polymer dispersed liquidcrystal, holographic polymer dispersed liquid crystal, polymer liquidcrystal, smectic liquid crystal, ferroelectric liquid crystal, andpolymer stabilized ferroelectric liquid crystal.

[0535] Further, it is obvious that birefringence can also be obtainedwith polymer materials other than liquid crystals by aligning the majoraxes of the polymer materials during forming.

[0536] [D-0039]

[0537] [Embodiment 17]

[0538]FIG. 55 shows other examples of the polarization type bifocaloptical system that can be used in the three-dimensional displays of thepreceding embodiments.

[0539] The polarization type bifocal optical system shown in FIG. 55comprises: a polarizing beam splitter 3401 for splitting a beam on theincoming side; two optical systems 3402, 3403 with different focallengths; a polarizing beam splitter 3404 for synthesizing on theoutgoing side; and plane mirrors 3405, 3406 for bending a light path.

[0540] The two optical systems 3402, 3403 are formed, for example, byconvex lens, concave lens, prism, convex/concave mirror or plane mirroror a combination of these.

[0541] In the polarization type bifocal optical system shown in FIG. 55,incident light is split by the polarizing beam splitter 3401 into twointrinsic polarized beams p41, p42 at a brightness ratio thatcorresponds to their polarization directions, and then fed into theoptical systems 3402, 3403.

[0542] The optical systems 3402, 3403 have different focal lengths andthus the incident polarized beams p41, p42 have different image formingdistances.

[0543] Therefore, when both of the polarized beams p41, p42 aresynthesized by the polarizing beam splitter 3404, the two intrinsicpolarized beams p41, p42 form images on different image focusing planes3407, 3408.

[0544] In this way, the optical system shown in FIG. 55 can form apolarization type bifocal optical system that can split light at abrightness ratio that corresponds to the polarization directions.

[0545] Here it is obvious that the similar effects can be produced if anoptical system including the configuration shown in FIG. 56 is usedinstead of the polarizing beam splitter 3401.

[0546] That is, the configuration of FIG. 56 includes polarizing plates3411, 3412 whose polarization directions are perpendicular to that ofthe beam splitter 3410 (e.g., semitransparent mirror and semitransparentprism). This configuration provides the similar effects.

[0547] It is also possible to use an optical system having theconfiguration shown in FIG. 56 instead of the polarizing beam splitter3404.

[0548] [D-0040]

[0549] [Embodiment 18]

[0550] The polarization varying device that can be used in thethree-dimensional displays of the preceding embodiments will beexplained.

[0551] A well known example of device that can change the polarizationdirection of incident light, as do the polarization varying devices usedin the three-dimensional displays of the preceding embodiments, is adevice that uses a medium (e.g., liquid crystals and PLZT) capable ofchanging birefringence by electric field and voltage.

[0552] Many kinds of devices using liquid crystals are described in“Liquid Crystals, Basics” and “Liquid Crystals, Applications” (by Okanoand Kobayashi, published by Baifukan).

[0553] Major examples are explained below by referring to FIGS. 57 to63A and 62B.

[0554]FIG. 57 shows the outline configuration of a twisted nematic typepolarization varying device that can be used in the three-dimensionaldisplays of the preceding embodiment.

[0555] The twisted nematic type polarization varying device shown inFIG. 57 includes a transparent conductive layer (transparent electrode)3501, an alignment layer 3502, a nematic liquid crystal region 3503, analignment layer 3504, and a transparent conductive layer (transparentelectrode) 3505.

[0556] It is common that the orientation directions of the alignmentlayers 3502 and 3504 are set perpendicular to each other and that achiral material is added so that the liquid crystal molecules aretwisted or describe a spiral in the same direction.

[0557] [D-0041]

[0558] As indicated by reference number 3510 in FIG. 58, when no voltageis applied between the transparent conductive films 3501 and 3505, thecrystal molecules rotate 90 degrees to described a spiral by theorientation restriction force of the alignment layers 3502, 3504 and theeffect of the chiral material.

[0559] The linearly polarized incident light therefore has itspolarization direction changed almost 90 degrees by the optical activityof the liquid crystals (one of the properties of the birefringentmaterial) before going out of the liquid crystals.

[0560] [D-0042]

[0561] When a voltage V5 sufficiently higher than the threshold voltageis applied between the transparent conductive films 3501 and 3505, theliquid crystal molecules are aligned in the voltage applicationdirection, as indicated by reference numeral 3511.

[0562] Hence, the incident light goes out almost without changing thepolarization direction.

[0563] When the voltage applied between the transparent conductive films3501 and 3505 is V5 or lower, a continuous change in polarizationdirection according to the applied voltage is obtained.

[0564] In this way, the polarization direction of the incident light canbe changed by the voltage applied between the transparent conductivefilms 3501 and 3505.

[0565] Further, it is also a well known practice to arrange theseconstitutional elements in matrix and drive them by using active driveelements.

[0566] [D-0043]

[0567]FIG. 59 shows the outline configuration of an in-plane typepolarization varying device that can be used in the two-dimensionaldisplays of the preceding embodiments.

[0568] The in-plane type polarization varying device includes atransparent conductive film (transparent electrode) 3601, an alignmentlayer 3602, a nematic liquid crystal region 3603, an alignment layer3604, and a transparent conductive film (transparent electrode) 3605.

[0569] Here the orientation directions of the alignment layer 3602 andthe alignment layer 3604 are parallel, and the transparent conductivefilms 3601 and 3605 are in the same plane.

[0570] As shown by reference numeral 3620 in FIG. 60, when no voltage isapplied between the transparent conductive films 3601, 3605, the liquidcrystal molecules are aligned in the orientation direction by theorientation restriction force of the alignment layers 3602, 3604.

[0571] When, as shown by reference numeral 3621 in FIG. 60, a voltage V6sufficiently higher than the threshold voltage is applied between thetransparent conductive films 3601 and 3605, the liquid crystal moleculesare aligned in the direction of voltage application.

[0572] Because the direction in which the liquid crystal moleculeshaving birefringence are aligned is changed in this way, thepolarization state of the exit light can be changed.

[0573] Further, when the voltage applied between the transparentconductive films 3601 and 3605 is V6 or lower, a continuous change inpolarization direction according to the applied voltage is obtained.

[0574] It is also a well known practice to arrange these constitutionalelements in matrix and drive them by using active drive elements.

[0575]FIG. 61 shows the outline configuration of a homogeneous typepolarization varying device that can be used in the three-dimensionaldisplays of the preceding embodiments.

[0576] The homogeneous type polarization varying device shown in FIG. 61includes a transparent conductive film (transparent electrode) 3611, analignment layer 3612, a liquid crystal (e.g., nematic liquid crystal)region 3613, an alignment layer 3614, and a transparent conductive film(transparent electrode) 3615.

[0577] In the homogeneous type polarization varying device shown in FIG.61, because homogeneously aligned liquid crystals are used, theorientation directions of the alignment layers 3612 and 3614 are setequal (parallel).

[0578] Further, in the homogeneous type polarization varying deviceshown in FIG. 61, light is entered whose polarization direction isdeviated from the orientation direction of the alignment layer.

[0579] For example, as shown in FIG. 62A, when incident light islinearly polarized, its polarization direction is shifted toward anintermediate direction between 0 and 90° (for example 45°) when thelight is thrown into the homogeneous type polarization varying deviceshown in FIG. 61.

[0580] Further, as shown in FIGS. 62B and 62C, incident light which iscircularly polarized or elliptically polarized is entered into thehomogeneous type polarization varying device shown in FIG. 61.

[0581] When, as shown in FIG. 63B, a voltage V7 sufficiently higher thanthe threshold voltage is applied between the transparent conductivefilms 3611 and 3615, the liquid crystal molecules are aligned in thedirection of voltage application.

[0582] Therefore, the incident light goes out almost without changingthe polarization direction.

[0583] On the other hand, when no voltage is applied between thetransparent conductive films 3611 and 3615, as shown in FIG. 63A, theliquid crystal molecules are aligned in the orientation direction by theorientation restriction force of the alignment layers 3612, 3614 andalso aligned parallel to the alignment layers 3612, 3614.

[0584] Therefore, the incident light goes out with its polarizationdirection changed by the birefringence of the liquid crystals.

[0585] Further, when the voltage applied between the transparentconductive layers 3611 and 3615 are V7 or lower, a continuous change inpolarization direction according to the applied voltage is obtained.

[0586] In this way, the polarization direction of the incident light canbe changed by the voltage applied between the transparent conductivefilms 3611 and 3615.

[0587] Further, it is also a well known practice to arrange theseconstitutional elements in matrix and drive them by using active driveelements.

[0588] There are apparently a variety of apparatuses that can use otherliquid crystals than nematic liquid crystal, such as ferroelectricliquid crystal, polymer dispersed liquid crystal and polymer liquidcrystal, and produce the similar effects.

[0589] Although the present invention has been described in detail inconjunction with preceding embodiments, it should be noted that theinvention is not limited to these embodiments and various modificationsmay be made without departing from the spirit of the invention.

[0590] [D-0044]

[0591] The representative advantages of this invention may be brieflysummarized as follows.

[0592] Contradictions among physiological factors associated withstereoscopy can be minimized; the amount of information required can bereduced; and electrically rewritable three-dimensional videos can bereproduced.

[0593] [E-0007]

[0594] [Embodiment 19]

[0595] In the following examples, a word “plane” on which to put animage is used. This is similar in meaning to an image plane that isoften used in optics. Means to realize such an image plane can obviouslybe realized by combining many optical devices, which include a varietyof optical elements (e.g., lens, total reflecting mirror, partialreflecting mirror, curved mirror, prism, polarizer and wavelength plate)and two-dimensional displays (e.g., CRT, liquid crystal display, LEDdisplay, plasma display, FED display, DMD display, projection typedisplay and line drawing type display).

[0596] The following examples concern a case where a three-dimensionalobject to be presented is displayed as two-dimensional images on mainlytwo planes. If the number of planes is increased to more than two, thesimilar effect can obviously be expected.

[0597]FIG. 64 shows the principle of a head-mounted display according toa nineteenth embodiment of the present invention.

[0598] In this embodiment a plurality of planes 4101, 4102 are set infront of an observer 4100 (with the plane 4101 put closer to theobserver 4100 than the plane 4102, for example). To display a pluralityof two-dimensional images on these planes, an optical system 4103 isconstructed by using two-dimensional displays and a variety of opticalelements.

[0599] (Details will be described in the twentieth and subsequentembodiment.)

[0600] Example two-dimensional displays include CRT, liquid crystaldisplay, LED display, plasma display, FED display, DMD display,projection type display and line drawing type display. Example opticalelements include lens, total reflecting mirror, partial reflectingmirror, curved mirror, prism, polarizer and wavelength plate.

[0601] The observer 4100 wears fixing means 4110 to fix relativepositions of a plurality of two-dimensional images displayed on theplanes 4101, 4102 with respect to left and right eyes of the observer4100.

[0602] [E-0008]

[0603] Next, as shown in FIG. 65, a three-dimensional object 4104 to bepresented to the observer 4100 is projected onto the planes 4101, 4102as seen from one point on a line connecting the left and right eyes ofthe observer 4100 to form two-dimensional images 4105, 4106.

[0604] The two-dimensional images can be generated by a variety of ways,which include a technique that photographs the object 4104 by camerafrom the one point described above; a technique that synthesizes aplurality of two-dimensional images photographed from differentdirections; or synthesizing and modeling techniques based on computergraphics.

[0605] The two-dimensional images 4105, 4106 are displayed on the planes4101, 4102 as shown in FIG. 64 so that they overlap each other as seenfrom the one point.

[0606] This can be achieved by putting the centers or gravity centers ofthe two-dimensional images 4105, 4106 on the line of sight.

[0607] [E-0009]

[0608] The important point of this embodiment is that, on the apparatushaving the above configuration, the brightness levels of thetwo-dimensional images are changed according to the depth position ofthe three-dimensional object 4104 while keeping constant the overallbrightness as seen by the observer 4100 (i.e., in such a way that theoverall brightness as seen by the observer 4100 is equal to thebrightness of the three-dimensional object 4104).

[0609] One example method of changing the brightness level is describedbelow.

[0610] FIGS. 66 to 69 are black and white illustrations and, forsimplicity, parts with higher brightness levels are shaded darker.

[0611] For example, when the three-dimensional object 4104 is displayedat a depth position corresponding to the position of the plane 4101, thebrightness of a two-dimensional image 4105 on the plane 4102 is setequal to that of the three-dimensional object 4104 and the brightness ofthe two-dimensional image 4106 on the plane 4102 is set to zero, asshown in FIG. 66.

[0612] Next, when the three-dimensional object 4104 moves slightly awayfrom the observer 4100 and is shown at a depth position slightly awayfrom the plane 4101 and closer to the plane 4102, the brightness of thetwo-dimensional image 4105 is slightly lowered and the brightness of thetwo-dimensional image 4106 is slightly raised, as shown in FIG. 67.

[0613] Further, when the three-dimensional object 4104 moves furtheraway from the observer 4100 and is shown at a depth position furtheraway from the plane 4101 and closer to the plane 4102, the brightness ofthe two-dimensional image 4105 is further lowered and the brightness ofthe two-dimensional image 4106 is further raised.

[0614] Finally, when the three-dimensional object 4104 is shown at adepth position corresponding to the position of the plane 4102, thebrightness of the two-dimensional image 4106 on the plane 4102 is setequal to that of the three-dimensional object 4104 and the brightness ofthe two-dimensional image 4105 on the plane 4101 is set to zero as shownin FIG. 69 for instance.

[0615] Displaying the object in this manner enables the observer 4100 tofeel as if the three-dimensional object 4104 is located between theplanes 4101 and 4102 because of observer's physiological or mentalfactors or optical illusion although what is actually shown to theobserver is the two-dimensional images 4105, 4106.

[0616] That is, when for example the two-dimensional images 4105, 4106with almost equal brightness are displayed on the planes 4101 and 4102,the three-dimensional object 4104 looks as if it lies near to a middlepoint between the depth positions of the planes 4101, 4102.

[0617] [E-0010]

[0618] Particularly when a point between the left and right eyes is usedas a viewing point on a line connecting the left and right eyes of theobserver 4100, the reliability for producing this effect is increased(or simply put, this same effect can be produced for a large number ofpeople or most of the time).

[0619] Further, when a center position between the left and right eyesof the observer 4100 is used as the viewing point, there is an advantagethat the same effect can be more readily produced and that the size of adouble image produced from the planes 4101, 4102 for both eyes can bereduced.

[0620] [E-0011]

[0621] The above description concerns a method and apparatus in whichthe overall depth position of the three-dimensional object 4104 isrepresented by using two-dimensional images on the planes 4101 and 4102.This embodiment apparently can be applied also as a method and apparatusthat represents the depth of the three-dimensional object itself.

[0622] In this case, the brightness level of each part of thetwo-dimensional images 4105, 4106 needs to be changed according to thedepth position of each corresponding part of the three-dimensionalobject 4104 while keeping constant the overall brightness as seen by theobserver 4100 (i.e., in such a way that the overall brightness as seenby the observer 4100 is equal to the brightness of the three-dimensionalobject 4104).

[0623] For example, the brightness of the two-dimensional image 4105displayed on the plane 4101 close to the observer 4100 is changedprogressively according to the depth position of the corresponding partof the object so that a portion close to the observer 4100 has a higherbrightness level and a portion remote from the observer has a lowerbrightness level.

[0624] The brightness of the two-dimensional image 4105 displayed on theplane 4102 remote from the observer 4100 is progressively changedaccording to the depth position of the corresponding part of the objectso that a portion close to the observer has a lower brightness level anda portion remote from the observer has a higher brightness level.

[0625] Displaying the object in this manner enables the observer 4100 tofeel as if the object presented has a solid body with some depth becauseof observer's physiological or mental factors or optical illusionalthough what is actually shown to the observer is two-dimensionalimages.

[0626] [E-0012]

[0627] Unlike the conventional apparatus (planar display), thisembodiment has at least two image display planes on the near and farsides of the optical illusion position, so that contradictions among thebinocular parallax, convergence and focusing—the problem experiencedwith the conventional apparatus—can be suppressed significantly, whichin turn is expected to reduce eyestrains.

[0628] As to the focusing, because the observer 4100 sees two or moreplanes simultaneously, the focus point coincides with the opticalillusion position where both of the images can be seen with minimumblur.

[0629] Further, because this embodiment can also present athree-dimensional object 4104 that exists between a plurality of planes,there is an advantage that the amount of data required forthree-dimensional representation can be reduced substantially.

[0630] Further, because the apparatus of this embodiment is fixedly wornby the observer 4100, this embodiment has the advantage of being able toeasily display two-dimensional images according to the movement of theobserver 4100 or eyes.

[0631] Although the head-mounted display is basically a display that issecured to the head of the wearer, the present invention can apparentlybe applied also to an apparatus that is not mounted on the head as longas the apparatus is so constructed that the positional relationshipbetween the eyes of the observer and the plane will not be changed.

[0632] Further, because this embodiment makes use of human physiologicalor mental factors or optical illusion based only on brightness changesof two-dimensional images, the embodiment does not require the use of acoherent light source such as a laser and facilitates the colorstereoscopic image representation.

[0633] Further, since this embodiment does not include mechanicaldriving parts, it can suitably reduce the weight of and improve thereliability of the apparatus.

[0634] This embodiment mainly concerns a case where there are only twoplanes for displaying two-dimensional images and where athree-dimensional object to be presented to the observer 4100 liesbetween the two planes. It is, however, apparent that the similarconfiguration can be employed if there are more planes or thethree-dimensional object 4104 to be presented is located at a differentposition.

[0635] [E-0013]

[0636] This embodiment can obviously display a video so that an observercan see the motion of an object in the horizontal and verticaldirections as long as the two-dimensional displays have display speedscompatible with the video. It is also apparent that the motion of anobject in the depth direction can also be presented to the observer bychanging the brightness of a plurality of planes for each frame.

[0637] In this case, the brightness of each part of the two-dimensionalimages 4105, 4106 is changed according to a change over time of thedepth position of the three-dimensional object 4104 while keepingconstant the overall brightness as seen by the observer 4100 (i.e., insuch a way that the overall brightness as seen by the observer 4100 isequal to the brightness of the three-dimensional object 4104).

[0638] That is, when for example the three-dimensional object 4104 is onthe plane 4101, the brightness of the two-dimensional image 4105 on theplane 4101 is set equal to that of the three-dimensional object 4104 andthe brightness of the two-dimensional image 4106 on the plane 4102 isset to zero.

[0639] [E-0014]

[0640] Next, when the three-dimensional object 4104 progressively movesslightly away from the observer 4100 and inches from the plane 4101toward the plane 4102 over time, the brightness of the two-dimensionalimage 4105 is lowered slightly over time according to the movement inthe depth position of the three-dimensional object 4104 and at the sametime the brightness of the two-dimensional image 4106 is slightly raisedover time.

[0641] Next, when the three-dimensional object 4104 moves further awayfrom the observer 4100 and inches from the plane 4101 further toward theplane 4102 over time, the brightness of the two-dimensional image 4105is lowered further over time according to the movement in the depthposition of the three-dimensional object 4104 and at the same time thebrightness of the two-dimensional image 4105 is raised further overtime.

[0642] Next, when the three-dimensional object 4104 finally reaches theplane 4102 over time, the brightness of the two-dimensional image 4106on the plane 4102 is changed over time until it becomes equal to thebrightness of the three-dimensional object 4104 according to themovement in the depth position of the three-dimensional object 4104 andat the same time the brightness of the two-dimensional image 4105 on theplane 4101 is changed over time until it becomes zero.

[0643] Displaying the object in this way enables the observer 4100 tofeel as if the three-dimensional object 4104 moves over time from theplane 4101 to the plane 4102 in the direction of depth because ofobserver's physiological or mental factors or optical illusion althoughwhat is actually shown to the observer is two-dimensional images 4105,4106.

[0644] It is obvious that, because of the after image effect, theabove-described effect of this embodiment can be produced as long as thetwo-dimensional images are displayed within one frame, whether they aredisplayed simultaneously or at different times, or displayedsimultaneously for one duration and separately for another duration.

[0645] Further, this embodiment has an advantage of being able tosignificantly reduce the amount of data required for three-dimensionalrepresentation because this embodiment can display a stereoscopicrepresentation of a three-dimensional object lying between a pluralityof planes.

[0646] [Embodiment 20]

[0647]FIG. 70 illustrates the principle of a head-mounted displayaccording to a twentieth embodiment of the invention.

[0648] In this embodiment, a plurality of planes, for example, planes1R1, 1R2, 1L1, 1L2 are arranged in front of the left and right eyes ofthe observer 4100 (the planes 1R1, 1L1 are set closer to the observer4100 than the planes 1R2, 1L2). To display a plurality oftwo-dimensional images on these planes, an optical system 4103 isconstructed for each of the left and right eyes by using two-dimensionaldisplays and a variety of optical elements. (Details will be describedin the twenty-first and subsequent embodiments.)

[0649] Examples of the two-dimensional displays include CRT, liquidcrystal display, LED display, plasma display, FED display, projectiontype display and line drawing type display. Examples of optical elementsinclude lens, total reflecting mirror, partial reflecting mirror, curvedmirror, prism, polarizer and wavelength plate.

[0650] The observer 4100 wears a fixing means 4110 to fix the relativepositions between the plurality of two-dimensional images displayed onthese planes 1R1, 1R2, 1L1, 1L2 and the left and right eyes of theobserver 4100.

[0651] [E-0015]

[0652] Next, as shown in FIG. 71, a three-dimensional object 4104 to bepresented to the observer 4100 is projected onto the planes 1R1, 1R2,1L1, 1L2, as viewed from one point on a line connecting the left andright eyes of the observer 4100, to form two-dimensional images 1R5,1R6, 1L5, 1L6.

[0653] While FIG. 71 shows the configuration for only the right eye, theconfiguration for the left eye can be obtained simply by replacing thesymbol R with L.

[0654] The two-dimensional images 1R5, 1R6, 1L5, 1L6 can be generated bya variety of ways, which include a technique that uses two-dimensionalimages obtained by photographing the three-dimensional object 4104 bycamera in the direction of line of sight; a technique that synthesizes aplurality of two-dimensional images photographed from differentdirections; or synthesizing and modeling techniques based on computergraphics.

[0655] The two-dimensional images 1R5, 1R6, 1L5, 1L6, as shown in FIG.70, are displayed on the planes 1R1, 1L1 and planes 1R2, 2L2 so thatthey overlap each other as seen from one point on the line connectingthe left and right eyes of the observer 4100.

[0656] This can be achieved by putting the centers or gravity centers ofthe two-dimensional images 1R5, 1R6, 1L5, 1L6 on the line of sight.

[0657] [E-0016]

[0658] The important point of this embodiment is that, in the apparatushaving the above-described configuration, the brightness of each of thetwo-dimensional images 1R5, 1R6, 1L5, 1L6 is changed within the afterimage time of the human eye according to the depth position of thethree-dimensional object 4104 (see FIG. 65) while keeping constant theoverall brightness as seen by the observer 4100 (i.e., in such a waythat the overall brightness as seen by the observer 4100 is equal to thebrightness of the three-dimensional object 4104.

[0659] One example method of changing the brightness is described below.

[0660] FIGS. 72 to 75 show the configuration for only the right eyebecause the same configuration applies also to the left eye. BecauseFIGS. 72 to 75 are black and white illustrations, parts with higherbrightness levels are shaded darker for simplicity.

[0661] When, for example, the three-dimensional object 4104 is displayedat a depth position corresponding to the positions of the planes 1R1,1L1, the brightness levels of the two-dimensional images 1R5, 1L5 on theplanes 1R1, 1L1 are set equal to the brightness level of thethree-dimensional object 4104 and the brightness levels of thetwo-dimensional images 1R6, 1L6 on the planes 1R2, 1L2 are set to zero,as shown in FIG. 72.

[0662] Next, when the three-dimensional object 4104 moves slightly awayfrom the observer 4100 and is displayed at a depth position slightlyaway from the planes 1R1, 1L1 and closer to the planes 1R2, 1L2, thebrightness levels of the two-dimensional images 1R5, 1L5 are slightlylowered and the brightness levels of the two-dimensional images 1R6, 1L6are slightly raised, as shown in FIG. 73.

[0663] Next, when the three-dimensional object 4104 moves further awayfrom the observer 4100 and is displayed at a depth position further awayfrom the planes 1R1, 1L1 and closer to the planes 1R2, 1L2, thebrightness levels of the two-dimensional images 1R5, 1L5 are furtherlowered and the brightness levels of the two-dimensional images 1R6, 1L6are further raised, as shown in FIG. 74.

[0664] Finally, when the three-dimensional object 4104 is displayed at adepth position corresponding to the planes 1R2, 1L2, the brightnesslevels of the two-dimensional images 1R6, 1L6 on the planes 1R2, 1L2 areset equal to the brightness level of the three-dimensional object 4104and the brightness levels of the two-dimensional images 1R5, 1L5 on theplanes 1R1, 1L1 are set to zero, as shown in FIG. 75.

[0665] Displaying the object in this manner enables the observer 4100 tofeel as if the three-dimensional object 4104 is located between theplanes 1R1, 1L1 and the planes 1R2, 1L2 because of human physiologicalor mental factors or optical illusion although what is actually shown tothe observer is the two-dimensional images 1R5, 1R6, 1L5, 1L6.

[0666] That is, when for example the two-dimensional images with almostequal brightness are displayed on the planes 1R1, 1L1 and the planes1R2, 1L2, the three-dimensional object 4104 looks as if it lies near toa middle point between the depth positions of the planes 1R1, 1L1 andthe planes 1R2, 1L2.

[0667] Particularly when a point between the left and right eyes is usedas a viewing point on a line connecting the left and right eyes of theobserver 4100, the reliability for producing this effect is increased(or simply put, this same effect can be produced for a large number ofpeople or most of the time).

[0668] Further, when a center position between the left and right eyesof the observer 4100 is used as the viewing point, there is an advantagethat the same effect can be more readily produced and that the size ofdouble image produced from the planes 1R1, 1L1 and planes 1R2, 1R2 forboth eyes can be reduced.

[0669] [E-0017]

[0670] As with the nineteenth embodiment, this embodiment can obviouslyexpress the depth of a three-dimensional object itself.

[0671] Unlike the conventional apparatus, this embodiment has at leasttwo image display planes on the near and far sides of the opticalillusion position, so that contradictions among the binocular parallax,convergence and focusing—the problem experienced with the conventionalapparatus—can be suppressed significantly, which in turn is expected toreduce eyestrains.

[0672] As to the focusing, because the observer 4100 sees two or moreplanes simultaneously, the focus point coincides with the opticalillusion position where both of the images can be seen with minimumblur.

[0673] In this embodiment, because the displays are mounted one for eacheye, there is an advantage that the two-dimensional images can bereadily displayed according to the movement of the observer or eyes.

[0674] Further, because this embodiment makes use of human physiologicalor mental factors or optical illusion based only on brightness changesof two-dimensional images, the embodiment does not require the use of acoherent light source such as a laser and facilitates the colorstereoscopic image representation.

[0675] Further, since this embodiment does not include mechanicaldriving parts, it can suitably reduce the weight of and improve thereliability of the apparatus.

[0676] This embodiment mainly concerns a case where there are only twoplanes for displaying two-dimensional images and where athree-dimensional object 4104 to be presented to the observer 4100 liesbetween the two planes. It is, however, apparent that the similarconfiguration can be employed if there are more planes or thethree-dimensional object 4104 to be presented is located at a differentposition.

[0677] Like the nineteenth embodiment, this embodiment can obviouslydisplay a video so that an observer can see the motion of an object inthe horizontal and vertical directions as long as the two-dimensionaldisplays have display speeds compatible with the video. It is alsoapparent that the motion of an object in the depth direction can also bepresented to the observer by changing the brightness of a plurality ofplanes for each frame.

[0678] It is obvious that, because of the after image effect, theabove-described effect of this embodiment can be produced as long as thetwo-dimensional images are displayed within one frame, whether they aredisplayed simultaneously or at different times, or displayedsimultaneously for one duration and separately for another duration.

[0679] Further, this embodiment has an advantage of being able tosignificantly reduce the amount of data required for three-dimensionalrepresentation because this embodiment can display a stereoscopicrepresentation of a three-dimensional object lying between a pluralityof planes.

[0680] [Embodiment 21]

[0681] An optical system 4103 that can be used in the precedingembodiments will be described.

[0682]FIG. 76 shows one example of the optical system 4103 that can beused in the preceding embodiments of the present invention.

[0683] The optical system 4103 shown in FIG. 76 employs a plurality oftwo-dimensional displays 4201, 4202, a total reflecting mirror 4203 (forexample, reflectivity/transmittivity=100/0), and a partial reflectingmirror 4204 (for example, reflectivity/transmittivity=50/50).

[0684] The plurality of two-dimensional displays 4201, 4202 are, forexample, CRT, liquid crystal display, LED display, plasma display, FEDdisplay, DMD display, projection type display and line drawing typedisplay.

[0685] In the optical system shown in FIG. 76, by changing thearrangement of the constitutional elements, it is possible to place twoplanes 4205, 4206 at different positions in the direction of depth, theplane 4205 being formed by reflecting a two-dimensional image of thetwo-dimensional display 4201 by the total reflecting mirror 4203 andpassing it through the partial reflecting mirror 4204, the plane 4206being formed by reflecting a two-dimensional image of thetwo-dimensional display 4202 by the partial reflecting mirror 4204.

[0686] In the optical system shown in FIG. 76, only mirrors (totalreflecting mirror 4203 and partial reflecting mirror 4204) are used,there is an advantage of less degradation of image quality.

[0687] [E-0018]

[0688]FIG. 77 illustrates another example of optical system 4103 thatcan be used in the preceding embodiments of the invention.

[0689] The optical system 4103 shown in FIG. 77, by including lenses4207, 4208 in the optical system shown in FIG. 76, makes it possible tochange the position of the planes more flexibly.

[0690] In the optical system shown in FIG. 77, which includes aplurality of two-dimensional displays 4201, 4202, a total reflectingmirror 4203 (for example, reflectivity/transmittivity=100/0), and apartial reflecting mirror 4204 (for example,reflectivity/transmittivity=50/50), convex lenses 4207, 4208 are addedto change the positions of the images, thus allowing more flexiblesetting of the positional relation between the plane 4205 and the plane4206 which has been restricted by the size of the apparatus.

[0691] As in the ordinary lens system, it may of course be advantageousin terms of distortion to use a combination lens in addition to convexlenses.

[0692] Further, although this embodiment has shown a case where virtualimages are used, it is obvious that the invention can also be applied toa case where real images are used.

[0693] [E-0019]

[0694]FIG. 78 shows a further example of optical system 4103 that can beused in the preceding embodiments of the invention.

[0695] The optical system 4103 shown in FIG. 78 incorporates additionaltwo-dimensional displays into the optical system shown in FIG. 76.

[0696] That is, a plurality of two-dimensional displays 4211, 4212,4213, 4214, 4215, a total reflecting mirror 4216 (e.g.,reflectivity/transmittivity=100/0) and partial reflecting mirrors 4217(e.g., reflectivity/transmittivity=50/50), 4218 (e.g.,reflectivity/transmittivity=33.3/66.7), 4219 (e.g.,reflectivity/transmittivity=25/75), 4220 (e.g.,reflectivity/transmittivity=20/80) are used to construct an opticalsystem.

[0697] In the optical system 4103 shown in FIG. 78, by changing thearrangements of these constitutional components, it is possible to placea plane 4221 and planes 4222-4225 at different positions in thedirection of depth, the image plane 4221 being formed by reflecting atwo-dimensional image of the two-dimensional display 4211 by the totalreflecting mirror 4216 and passing it through the partial reflectingmirrors 4217-4220, the planes 4222-4225 being formed by reflectingtwo-dimensional images of the two-dimensional displays 4212-4215 by thepartial reflecting mirrors 4217-4220 and passing them through thesepartial reflecting mirrors.

[0698] This optical system 4103 shown in FIG. 78 uses only mirrors andthus has the advantage of less degradation of picture quality.

[0699] While FIG. 78 shows a case where there are five two-dimensionaldisplays, it is apparent that the similar configuration can be adoptedwhen a different number of two-dimensional displays are used.

[0700] In this case also, it is obvious that adding lens systems asshown in FIGS. 77 makes it easy to control the positions of planes.

[0701] [E-0020]

[0702]FIG. 79 shows a further example of the optical system 4103 thatcan be used in the preceding embodiments of the invention.

[0703] The optical system 4103 shown in FIG. 79 uses a plurality ofprojector type two-dimensional displays 4231, 4232, 4233, 4234, 4235,shutters 4241, 4242, 4243, 4244, 4245, and scatter plates 4236, 4237,4238, 4239, 4240 to project two-dimensional images from the projectortype two-dimensional displays 4231-4235 through the shutters 4236-440onto the scatter plates 4236-4240 to produce the two-dimensional imagesat desired locations.

[0704] The projector type two-dimensional displays 4231-4235 are, forexample, of CTR type, LCD type, ILV type, DMD type, etc.

[0705] The scatter plates 4236-4240 are, for example, such devices ascan control scattering/transmission or reflection/transmission, such aspolymer dispersed liquid crystal devices, holographic polymer dispersedliquid crystal devices or combined devices of liquid crystal andmulti-lens array. Shutters 4241-4245 may be such devices as can controltransmission/interruption, such as twisted nematic liquid crystaldevices, ferroelectric liquid crystal devices or mechanical shutterdevices.

[0706] The scatter plates 4236-4240 are arranged at different depthpositions, the focusing planes of the projector type two-dimensionaldisplays 4231-4235 are aligned with these scatter plates 4236-4240,two-dimensional images are projected onto the scatter plates, and thescattering/transmission timing of the scatter plates 4236-4240 issynchronized with the transmission/interruption timing of the shutters4241-4245 when activating the scatter plates and the shutters. Thisenables the depth positions of the planes 4241-4245 formed on thescatter plates 4236-4240 to be controlled on a time division basis.

[0707] Like the optical system 4103 shown in FIG. 79, the use ofprojector type two-dimensional displays 4231-4235 provides an advantageof enhanced level of freedom of display layout.

[0708] Although the optical system 4103 of FIG. 79 concerns a case wherethere are five projector type two-dimensional displays, it is apparentthat the similar configuration can be employed when a different numberof displays are provided.

[0709] It is obvious that the lamps of projector type two-dimensionaldisplays 4231-4235 can be turned on or off instead of using theshutters.

[0710] [E-0021]

[0711] In the preceding embodiments, we have mainly described a casewhere the planes are located near, inside or beyond the head-mounteddisplays. Incorporation of optical devices enables these planes to beeasily arranged away from or in front of the two-dimensional displays.

[0712] One such example is shown in FIG. 80.

[0713] For example, it can easily be seen that by arranging a lenssystem 4303 in front of the optical system 4301 shown in the precedingembodiments, the internal planes 4302 can be moved to the positions ofexternal planes 4304.

[0714] This offers the advantage that because the three-dimensionalimages are reproduced floating in space, the three-dimensional imagesare more likely to appear three-dimensional to the observer than whenthe three-dimensional images are located inside or behind the display.

[0715] The invention has been described in detail in conjunction withthe preceding embodiments and it should be noted that the invention isnot limited to these embodiments and that various modifications may bemade without departing from the spirit of the invention.

[0716] [E-0022]

[0717] The representative advantages of this invention may be brieflysummarized as follows.

[0718] Contradictions among physiological factors associated withstereoscopy can be minimized; the amount of information required can bereduced; and electrically rewritable three-dimensional videos can bereproduced.

[0719] [F-0001]

[0720] [Embodiment 22]

[0721]FIGS. 81A and 81B show the concept of a twenty-second embodimentof the invention.

[0722]FIG. 81A illustrates a three-dimensional display 5101 which allowsa plurality of observers 5102, 5103, 5104 to simultaneously view athree-dimensional image displayed on the three-dimensional display 5101,by putting reflectors 5105, 5106, 5107 at different angles on theoptical axis of the three-dimensional display to reflect thethree-dimensional image toward the observers. The reflectors 5105, 5106,5107 used are, for example, half mirrors or prisms, which can performreflection or refraction and transmission at the same time. Thereflector 5107 alone may use a total reflecting mirror.

[0723]FIG. 81B illustrates a three-dimensional display 5111 which allowsa plurality of observers 5112, 5113, 5114 to simultaneously view athree-dimensional image displayed on the three-dimensional display 5111,by putting reflectors 5115, 5116, 5117 at different angles on theoptical axis of the three-dimensional display to reflect thethree-dimensional image toward the observers. Optical systems 5118,5119, 5120 arranged on optical axes connecting the observers and thereflectors cause the three-dimensional image displayed on thethree-dimensional display 5111 to be focused on an image plane 5121 sothat all the observers can view the three-dimensional image at the sameposition (image plane 5121). The reflectors 5115, 5116, 5117 used are,for example, half mirrors or prisms, which can perform reflection orrefraction and transmission at the same time. The reflector 5117 alonemay use a total reflecting mirror.

[0724] With this simple method, a three-dimensional display that allowsa plurality of observers to view an image simultaneously can berealized.

[0725] [Embodiment 23]

[0726]FIGS. 82A and 82B illustrate the concept of a twenty-thirdembodiment of the invention.

[0727]FIG. 82A illustrates a three-dimensional display, which displays athree-dimensional image by using two displays 5201 and 5202 and whichincludes reflectors 5206, 5207, 5208 and reflectors 5209, 5210, 5211arranged at different angles on two optical axes of the two displays toreflect two images of the two displays along the same optical axistoward each of a plurality of observers 5203, 5204, 5205 so that eachobserver can view the two images overlapping each other and all theobservers can view the same overlapping images at the same time. Thereflectors 5206, 5207, 5208, 5209, 5210, 5211 are, for example, halfmirrors or prisms, which can perform reflection or refraction andtransmission at the same time. The reflector 5208 alone may use a totalreflecting mirror.

[0728]FIG. 82B illustrates a three-dimensional display, which displays athree-dimensional image by using two displays 5221 and 5222 and whichincludes reflectors 5226, 5227, 5228 and reflectors 5229, 5230, 5231arranged at different angles on two optical axes of the two displays toreflect two images of the two displays along the same optical axistoward each of a plurality of observers 5223, 5224, 5225 so that eachobserver can view the two images overlapping each other and all theobservers can view the same overlapping images at the same time. Opticalsystems 5232, 5233, 5234 arranged on optical axes connecting theobservers and the reflectors cause a three-dimensional image displayedby the two displays 5221, 5222 to be focused on an image plane 5235 sothat all the observers can view the three-dimensional image at the sameposition (image plane 5235). The reflectors 5226, 5227, 5228, 5229,5230, 5231 are, for example, half mirrors or prisms, which can performreflection or refraction and transmission at the same time. Thereflector 5228 alone may use a total reflecting mirror.

[0729] With this simple method, a three-dimensional display that allowsa plurality of observers to view an image simultaneously can berealized.

[0730] [Embodiment 24]

[0731]FIGS. 83A and 83B illustrate the concept of a twenty-fourthembodiment of the invention.

[0732]FIG. 83A shows a three-dimensional display 5301, which includesreflectors 5305, 5306, 5307 arranged at different angles on an opticalaxis of the three-dimensional display to reflect a three-dimensionalimage toward each of a plurality of observers 5302, 5303, 5304 so thatall the observers can view the three-dimensional image simultaneously.The reflectors 5305, 5306, 5307 may use, for example, dichroic mirror,dichroic prism and holographic optical element, which can limit thewavelength to be reflected and can perform reflection and transmissionat the same time. The reflector 5307 alone can use a total reflectingmirror. By shifting the reflection wavelength of each reflector to adegree that will not result in a significant change in color, all theobservers can view almost the same three-dimensional image. Colorrepresentation can be provided by stacking reflectors of three primarycolors (R, G, B) (for example, stacking three red, green and bluereflectors at the position of reflector 5305).

[0733]FIG. 83B illustrates a three-dimensional display, which displays athree-dimensional image by using two displays 5311 and 5312 and whichincludes reflectors 5316, 5317, 5318 and reflectors 5319, 5320, 5321arranged at different angles on two optical axes of the two displays toreflect two images of the two displays along the same optical axistoward each of a plurality of observers 5313, 5314, 5315 so that eachobserver can view the two images overlapping each other and all theobservers can view a three-dimensional image at the same time. Thereflectors 5316, 5317, 5318, 5319, 5320, 5321 may use, for example,dichroic mirror, dichroic prism and holographic optical element, whichcan limit the wavelength to be reflected and can perform reflection andtransmission at the same time. The reflector 5318 alone can use a totalreflecting mirror. By shifting the reflection wavelength of eachreflector to a degree that will not result in a significant change incolor, all the observers can view almost the same three-dimensionalimage. Color representation can be provided by stacking reflectors ofthree primary colors (R, G, B) (for example, stacking three red, greenand blue reflectors at the position of reflector 5316). The pairedreflectors (e.g., reflector 5316 and reflector 5319) may have the sameband of wavelength.

[0734] This configuration is possible even when mirrors are overlappingeach other on an optical axis.

[0735] [Embodiment 25]

[0736]FIGS. 84A and 84B show the concept of a twenty-fifth embodiment ofthe invention.

[0737]FIG. 84A shows a three-dimensional display, which includes aviewing zone distributor 5407 to distribute an optical axis from thethree-dimensional display 5401 into a plurality of optical axes andrefract light from the three-dimensional display toward each of aplurality of observers 5402, 5403, 5404, 5405, 5406 so that all theobservers can simultaneously view the same three-dimensional imagedisplayed on the three-dimensional display. Among example devices usedfor the viewing zone distributor 5407 are a holographic optical elementthat has a plurality of diffraction angles and can diffract rays oflight at different angles at the same time, a prism array 5421 such asshown in FIG. 84C, and a diffraction grating array 5441 such as shown inFIG. 84E. The prism array 5421 has a number of small prisms 5422 withdifferent refraction directions to refract and distribute light from thethree-dimensional display toward each of the observers. Likewise, thediffraction grating array 5441 has a number of small diffractiongratings 5442 with different sizes of gratings to diffract anddistribute light from the three-dimensional display toward each of theobserver.

[0738]FIG. 84B shows a three-dimensional display, which includes aviewing zone distributor 5417 to distribute an optical axis from thethree-dimensional display 5411 into a plurality of optical axes andreflect light from the three-dimensional display toward each of aplurality of observers 5412, 5413, 5414, 5415, 5416 so that all theobservers can simultaneously view the same three-dimensional imagedisplayed on the three-dimensional display. Among example devices usedfor the viewing zone distributor 5417 are a holographic optical elementthat has a plurality of reflection angles and can reflect rays of lightat different angles at the same time, a mirror array 5431 such as shownin FIG. 84D, and a diffraction grating array 5441 such as shown in FIG.84E. The mirror array 5431 has a number of small mirrors 5432 withdifferent reflection directions to reflect light from thethree-dimensional display toward each of the observers. Likewise, thediffraction grating array 5441 has a number of small diffractiongratings 5442 with different sizes of gratings to reflect and distributelight from the three-dimensional display toward each of the observer.

[0739] This arrangement can expand a viewing zone of an observer whilemoving or a viewing zone for a plurality of observers.

[0740] [Embodiment 26]

[0741]FIGS. 85A and 85B show the concept of a twenty-sixth embodiment ofthe invention.

[0742]FIG. 85A shows a three-dimensional display, which includes aviewing zone distributor 5507 to distribute an optical axis from thethree-dimensional display 5501 into a plurality of optical axes andrefract light from the three-dimensional display toward each of aplurality of observers 5502, 5503, 5504, 5505, 5506 so that all theobservers can simultaneously view the same three-dimensional imagedisplayed on the three-dimensional display. The viewing zone distributor5507 uses a plurality of holographic optical elements stacked togethereach of which can diffract light at only one angle. The holographicoptical elements 5508, 5509, 5510, 5511, 5512 with different diffractionangles are stacked together to diffract light from the three-dimensionaldisplay toward the respective observers.

[0743]FIG. 85B shows a three-dimensional display, which includes aviewing zone distributor 5527 to distribute an optical axis from thethree-dimensional display 5521 into a plurality of optical axes andreflect light from the three-dimensional display toward each of aplurality of observers 5522, 5523, 5524, 5525, 5526 so that all theobservers can simultaneously view the same three-dimensional imagedisplayed on the three-dimensional display. The viewing zone distributor5527 uses a plurality of holographic optical elements stacked togethereach of which can diffract light at only one angle. The holographicoptical elements 5528, 5529, 5530, 5531, 5532 with different reflectionangles are stacked together to distribute light from thethree-dimensional display toward the respective observers.

[0744] This arrangement can expand a viewing zone of an observer whilemoving or a viewing zone for a plurality of observers.

[0745] [Embodiment 27]

[0746]FIGS. 86A to 86D show the concept of a twenty-seventh embodimentof the invention.

[0747]FIG. 86A illustrates a three-dimensional display, which includes aviewing zone distributor 5607 to distribute an optical axis from thethree-dimensional display 5601 into a plurality of optical axes on atime division basis and refract light from the three-dimensional displaytoward each of a plurality of observers 5602, 5603, 5604, 5605, 5606 sothat all the observers can view the same three-dimensional image. Theviewing zone distributor 5607 uses a liquid crystal deflection elementwhich comprises a liquid crystal and an optical element disposed incontact with the liquid crystal. The liquid crystal deflection elementdeflects light from the three-dimensional display at high speed withinthe after image time of human eye between observer 5602 and observer5606 to distribute light to individual observers. When the light, whilebeing deflected, reaches the direction of an observer, it is haltedtemporarily at that position and then deflected toward the nextobserver. This process is repeated at high speed allowing the observersto see a three-dimensional image.

[0748]FIG. 86B illustrates a three-dimensional display, which includes aviewing zone distributor 5617 and a reflector 5618 to distribute anoptical axis from the three-dimensional display 5611 into a plurality ofoptical axes on a time division basis and reflect light from thethree-dimensional display toward each of a plurality of observers 5612,5613, 5614, 5615, 5616 so that all the observers can view the samethree-dimensional image. The viewing zone distributor 5617 uses a liquidcrystal deflection element which comprises a liquid crystal and anoptical element disposed in contact with the liquid crystal. The liquidcrystal deflection element deflects light from the three-dimensionaldisplay at high speed within the after image time of human eye betweenobserver 5612 and observer 5616 to distribute light to individualobservers. When the light, while being deflected, reaches the directionof an observer, it is halted temporarily at that position and thendeflected toward the next observer. This process is repeated at highspeed allowing the observers to see a three-dimensional image. Thereflector 5618 uses such reflecting material as mirror.

[0749]FIG. 86C illustrates a three-dimensional display, which includes aviewing zone distributor 5627 to distribute an optical axis from thethree-dimensional display 5621 into a plurality of optical axes on atime division basis and refract light from the three-dimensional displaytoward each of a plurality of observers 5622, 5623, 5624, 5625, 5626 sothat all the observers can view the same three-dimensional image. Theviewing zone distributor 5627 uses a liquid crystal deflection elementwhich comprises a liquid crystal and an optical element disposed incontact with the liquid crystal. The liquid crystal deflection elementdeflects light from the three-dimensional display at high speed withinthe after image time of human eye between observer 5622 and observer5626 to distribute light to individual observers. A shutter 5628 isoperated at the same time that the refraction direction of the viewingzone distributor 5627 aligns with the direction of each observer, thusallowing the observers to see a three-dimensional image.

[0750]FIG. 86D illustrates a three-dimensional display, which includes aviewing zone distributor 5637 and a reflector 5638 to distribute anoptical axis from the three-dimensional display 5631 into a plurality ofoptical axes on a time division basis and reflect light from thethree-dimensional display toward each of a plurality of observers 5632,5633, 5634, 5635, 5636 so that all the observers can view the samethree-dimensional image. The viewing zone distributor 5637 uses a liquidcrystal deflection element which comprises a liquid crystal and anoptical element disposed in contact with the liquid crystal. The liquidcrystal deflection element deflects light from the three-dimensionaldisplay at high speed within the after image time of human eye betweenobserver 5632 and observer 5636 to distribute light to individualobservers. A shutter 5639 is operated at the same time that therefraction direction of the viewing zone distributor 5637 aligns withthe direction of each observer, thus allowing the observers to see athree-dimensional image. The reflector 5638 uses such reflectingmaterial as mirror.

[0751] This apparatus can also be used for expanding a viewing zone ofan observer when he or she moves.

[0752] [Embodiment 28]

[0753]FIGS. 87A and 87B show the concept of a twenty-eighth embodimentof the invention.

[0754]FIG. 87A illustrates a three-dimensional display, which includes areflector 5707 to distribute an optical axis from the three-dimensionaldisplay 5701 into a plurality of optical axes on a time division basisand reflect/refract light from the three-dimensional display toward eachof a plurality of observers 5702, 5703, 5704, 5705, 5706 so that all theobservers can view the same three-dimensional image. Among devices usedfor the reflector 5707 are a half mirror, a total reflecting mirror anda prism. The reflector 5707 deflects light from the three-dimensionaldisplay at high speed within the after image time of human eye betweenobserver 5702 and observer 5706 to distribute light to individualobservers. Light distribution can be achieved by reciprocating thereflector to left and right at high speed or by rotating it in onedirection. When the light, while being deflected, reaches the directionof an observer, it is stopped temporarily at that position and thendeflected toward the next observer. This process is repeated at highspeed allowing the observers to see a three-dimensional image.

[0755]FIG. 87B illustrates a three-dimensional display, which includes areflector 5717 to distribute an optical axis from the three-dimensionaldisplay 5711 into a plurality of optical axes on a time division basisand reflect/refract light from the three-dimensional display toward eachof a plurality of observers 5712, 5713, 5714, 5715, 5716 so that all theobservers can view the same three-dimensional image. Among devices usedfor the reflector 5717 are a half mirror, a total reflecting mirror anda prism. The reflector 5717 deflects light from the three-dimensionaldisplay at high speed within the after image time of human eye betweenobserver 5712 and observer 5716 to distribute light to individualobservers. Light distribution can be achieved by reciprocating thereflector to left and right at high speed or by rotating it in onedirection. A shutter 5718 is operated at the same time that thereflection/refraction direction of light, while being deflected, alignswith the direction of each observer, thus allowing the observers to seea three-dimensional image.

[0756] This arrangement can expand a viewing zone of an observer whilemoving or a viewing zone for a plurality of observers.

[0757] The present invention has been described in detail in conjunctionwith example embodiments. It should be noted that the invention can beapplied not only to the above-described three-dimensional displays butalso as a means to expand a narrow viewing zone in generalthree-dimensional displays or stereoscopic displays. It should also benoted that the invention is not limited to these embodiments but variousmodifications may be made without departing from the spirit of theinvention.

[0758] The representative advantages of this invention may be brieflysummarized as follows.

[0759] In three-dimensional displays or stereoscopic displays withnarrow viewing zones, the viewing zone distributor installed todistribute a viewing zone from the display to a plurality of otherdirections allows expansion of the viewing zone or increase in thenumber of viewing zones, which in turn makes it possible for a pluralityof people to simultaneously view the displayed image or for a movingobserver to view the image.

[0760] In a three-dimensional display which generates athree-dimensional image by displaying on a plurality of image planes atdifferent depth positions two-dimensional images with brightness levelswhose ratio corresponds to the depth position of each part of an objectto be presented, the viewing zone distributor installed to distributethe viewing zone from the display into a plurality of other directionsallows expansion of the viewing zone while keeping the misalignmentbetween the front and rear displayed images at a low level that does notappear incongruous to the observer. The provision of the viewing zonedistributor also allows the three-dimensional image to be viewed by aplurality of observers simultaneously or to be seen by the observerwhile moving.

[0761] [F-0002]

[0762] [Center of Overlapping Two-Dimensional Images]

[0763] In the preceding embodiments, the phenomenon of this inventionoccurs when the sizes of two-dimensional images on the front and rearplanes are controlled so that these two-dimensional images overlap asseen with the visual acuity of the observer from one point on a lineconnecting the left and right eyes of the observer. More preciselyspeaking, the essential requirement for this phenomenon is that thetwo-dimensional images must overlap in the vertical direction as viewedwith the visual acuity of the observer from one point on a lineconnecting the left and right eyes of the observer.

[0764] This is explained by referring to FIGS. 88A to 88C. The bestviewing position is at a middle point between the left and right eyes,as shown in FIG. 88A. This is because the double image of edge portionsas seen from both eyes are smallest in this case. The viewing positionfrom which the phenomenon of the invention can be observed is betweenboth eyes, and the extreme allowable position is as shown in FIG. 88B.There is a possibility, however, that this phenomenon can still beobserved even when the viewing position goes outside both eyes by asmall amount undistinguishable from FIG. 88B and stays within the visualacuity of the observer, as shown in FIG. 88C. When the viewing positionmoves further away, this phenomenon generally cannot be observedcorrectly, with the displayed images perceived as two separate front andrear two-dimensional images.

[0765] [Coloring of Overlapping Two-Dimensional Images]

[0766] With this invention, the apparent depth position of a perceivedthree-dimensional image can be changed by changing the ratio ofbrightness levels of the front and rear two-dimensional images. Hence,as shown in FIG. 89, the color of the front two-dimensional image (e.g.,red in FIG. 89) and the color of the rear two-dimensional image (e.g.,green in FIG. 89) can be differentiated from each other in such a waythat the three-dimensional image that is perceived by the observer whenhe sees these overlapping two-dimensional images has the intended colorto be presented (e.g., yellow in FIG. 89).

[0767] [Distance Between Planes]

[0768] The phenomenon of the present invention is produced when thereare overlapping portions of the front and rear two-dimensional images inthe right-eye image and in the left-eye image, as shown in FIG. 90A.Hence, when the front and rear planes are set apart by a great distanceand the front and rear two-dimensional images do not overlap and areseparated in the right-eye image and in the left-eye image, as shown inFIG. 90B, the phenomenon of interest is not generated and the observerperceives two separate front and rear two-dimensional images.

[0769] [F-0003]

[0770] Another example of the embodiment 28 is explained by referring toFIGS. 91A and 91B. FIG. 91A illustrates an example case where athree-dimensional virtual image is produced. FIG. 91B illustrates anexample case where a three-dimensional real image is generated. Thisembodiment includes a two-dimensional display (for example, CRT, liquidcrystal display, LED display, PDP and FED), a varifocal lens (forexample, dual-frequency type: see Japanese Patent Application182222/1996 titled “Optical Apparatus”; high-voltage liquid crystaltype: see Japanese Patent Application 202244/1996 titled “OpticalApparatus”; polarizing multifocal type; and liquid crystal motor type:see Japanese Patent Application 301600/1997 titled “Optical Apparatus”),an optical system (for example, concave lens, convex lens, concavemirror, convex mirror, total reflecting mirror, partial reflectingmirror, and prism).

[0771] The varifocal lens, a key device in this embodiment, can changeits focal length at high speed and therefore can focus a displayed imageof the two-dimensional display at different depth positions. Therefore,by synchronizing a change in the focal length of the varifocal lensdriven by a driving device with an image display timing of thetwo-dimensional display by a synchronizing device and also by writingthe images at all depth positions within the after image time, it ispossible to provide a three-dimensional representation in a depthsampling manner.

[0772] The present invention has been described in detail with respectto preferred embodiments, and it will now be apparent from the foregoingto those skilled in the art that changes and modification may be madewithout departing from the invention in its broader aspect, and it isthe invention, therefore, in the apparent claims to cover all suchchanges and modification as fall within the true spirit of theinvention.

What is claimed is:
 1. A three-dimensional representation method forgenerating a three-dimensional image by displaying two-dimensionalimages on a plurality of image planes located at different depthpositions, the method comprising the steps of: generatingtwo-dimensional images in which an object to be presented is projectedalong the line of sight of an observer, onto a plurality of image planeslocated at different depth positions as seen from the observer; andchanging brightness levels of the generated two-dimensional imagesindividually for each image plane to display the generatedtwo-dimensional images on the plurality of image planes.
 2. Athree-dimensional representation method as claimed in claim 1, wherein,when the object to be presented is displayed at a depth position closeto the observer, the brightness levels of the two-dimensional imagesdisplayed on those image planes of the plurality of image planes whichare close to the observer are raised and the brightness levels of thetwo-dimensional images displayed on the image planes remote from theobserver are lowered, and wherein, when the object to be presented isdisplayed at a depth position remote from the observer, the brightnesslevels of the two-dimensional images displayed on those image planes ofthe plurality of image planes which are close to the observer arelowered and the brightness levels of the two-dimensional imagesdisplayed on the image planes remote from the observer are raised.
 3. Athree-dimensional representation method as claimed in claim 1, whereinthe two-dimensional images are displayed on the plurality of imageplanes in such a way that the two-dimensional images overlap each otherwhen the two-dimensional images are viewed from one point on a linewhich passes through the right and left eyes of an observer, and that anoverall brightness level as seen by the observer is equal to thebrightness level of the original object to be presented.
 4. Athree-dimensional representation method as claimed in claim 3, whereinthe point on the line which passes through the right and left eyes ofthe observer is one point between the right and left eyes.
 5. Athree-dimensional representation method as claimed in claim 3, whereinthe point on the line which passes through the right and left eyes ofthe observer is the point of the center between the right and left eyes.6. A three-dimensional representation method as claimed in claim 1,wherein the two-dimensional images are arranged to overlap by viewingfrom one point on the line which passes through the right and left ofthe observer and the two-dimensional images are enlarged or reduced inthe horizontal direction respectively.
 7. A three-dimensionalrepresentation method as claimed in claim 2, wherein the two-dimensionalimages are displayed on the plurality of image planes in such a way thatthe two-dimensional images overlap each other when the two-dimensionalimages are viewed from one point on the line which passes through theright and left eyes of the observer and wherein when the depth positionof the object to be presented is remote from the observer, an overallbrightness level as seen by the observer is set lower than thebrightness level of the original object when the depth position of theobject is close.
 8. A three-dimensional representation method as claimedin claim 1, wherein the two-dimensional images are switched successivelyto generate a three-dimensional moving image.
 9. A three-dimensionalrepresentation method as claimed in claim 8, wherein when thetwo-dimensional images include a plurality of images of an object movingin a direction of depth and the object is moving toward the observer,the brightness levels of the object images displayed on the plurality ofimage planes are progressively raised toward an image plane close to theobserver and progressively lowered toward an image plane remote from theobserver in synchronism with the successive switching of thetwo-dimensional images, and wherein when the two-dimensional imagesinclude a plurality of images of an object moving in a direction ofdepth and the object is moving away from the observer, the brightnesslevels of the object images displayed on the plurality of image planesare progressively lowered toward an image plane close to the observerand progressively raised toward an image plane remote from the observerin synchronism with the successive switching of the two-dimensionalimages.
 10. A three-dimensional representation method as claimed inclaim 1, wherein distances of depth between the image planes are withina range having a common area in the case that a plurality oftwo-dimensional images are viewed by a single eye of the observer at theposition of the right and left eyes of the observer, the plurality oftwo-dimensional images being displayed on the image planes for the sameobject to be presented.
 11. A three-dimensional representation method asclaimed in claim 1, wherein the colors of the plurality oftwo-dimensional objects to be presented in the two-dimensional imagesare different each other, the color of a three-dimensional object to berepresent is determined according to the different colors and the colorsof the plurality of the two-dimensional objects is possible to changewithout changing the determined color which is viewed by the observer.12. A three-dimensional display comprising: a first means for generatingtwo-dimensional images in which an object to be presented is projectedalong the line of sight of an observer, onto a plurality of image planeslocated at different depth positions as seen from the observer; a secondmeans for displaying the two-dimensional images generated by the firstmeans on the plurality of image planes located at different depthpositions as seen from the observer; and a third means for changingbrightness levels of the two-dimensional images displayed on theplurality of image planes individually for each image plane.
 13. Athree-dimensional display as claimed in claim 12, wherein the secondmeans comprises: a plurality of two-dimensional displays; and partialreflecting mirrors combined with the plurality of two-dimensionaldisplays except for one two-dimensional display located at the remotestdepth position from the observer, the partial reflecting mirrors beingadapted to locate images of the two-dimensional displays on the line ofsight of the observer.
 14. A three-dimensional display as claimed inclaim 12, wherein the second means comprises: a plurality oftwo-dimensional displays; and combinations of partial reflecting mirrorsand lenses, the partial reflecting mirror and lens combinations beingcombined with the plurality of two-dimensional displays except for onetwo-dimensional display located at the remotest depth position from theobserver, the partial reflecting mirror and lens combinations beingadapted to locate images of the two-dimensional displays on the line ofsight of the observer.
 15. A three-dimensional display as claimed inclaim 12, wherein the second means comprises: a plurality oftwo-dimensional displays; a total reflecting mirror or partialreflecting mirror combined with one of the plurality of two-dimensionaldisplays which is located at the remotest depth position from theobserver, the total reflecting mirror or partial reflecting mirror beingadapted to locate an image of the one two-dimensional display on theline of sight of the observer; and partial reflecting mirrors combinedwith the two-dimensional displays except for the one two-dimensionaldisplay located at the remotest depth position from the observer, thepartial reflecting mirrors being adapted to locate images of thetwo-dimensional displays on the line of sight of the observers.
 16. Athree-dimensional display as claimed in claim 12, wherein the secondmeans comprises: a plurality of two-dimensional displays; a combinationof a total reflecting mirror and a lens or a combination of a partialreflecting mirror and a lens, the combination being combined with one ofthe plurality of two-dimensional displays which is located at theremotest depth position from the observer, the combination being adaptedto locate an image of the one two-dimensional display on the line ofsight of the observer; and combinations of partial reflecting mirrorsand lenses, the combinations being combined with the two-dimensionaldisplays except for one two-dimensional display located at the remotestdepth position from the observer, the combinations being adapted tolocate images of the two-dimensional displays on the line of sight ofthe observer.
 17. A three-dimensional display as claimed in claim 12,wherein the second means comprises: a plurality of scatter platescapable of controlling a switching between a transmitting state and ascattering state or a plurality of reflection plates capable ofcontrolling the switching between a reflecting state and a transmittingstate, the scatter plates or reflection plates being located atdifferent depth positions as viewed from the observer; a plurality ofprojection type two-dimensional displays for projecting two-dimensionalimages onto the plurality of scatter plates or the plurality ofreflection plates; and a plurality of shutters disposed between theplurality of scatter plates or reflection plates and the plurality ofprojection type two-dimensional displays, the plurality of shuttersbeing adapted to switch between a transmitting state and a cutoff statein synchronism with the switching between the transmitting state and thescattering state of the plurality of scatter plates or between thereflecting state and the transmitting state of the plurality ofreflection plates.
 18. A three-dimensional display as claimed in claim12, wherein a lens optical system is disposed between the observer andthe plurality of image planes located at different depth positions asseen from the observer.
 19. A three-dimensional display as claimed inclaim 12, wherein the second means comprises: a two-dimensional display;an optical system; and a varifocal mirror.
 20. A three-dimensionaldisplay as claimed in claim 12, wherein the second means comprises: avibration screen which vibrates in the direction of depth; an opticalsystem including a lens; a scanning means for raster-scanning a laserbeam; and a laser beam source.
 21. A three-dimensional display asclaimed in claim 12, wherein the second means comprises: an LED displayhaving an LED array; a parallel advancing/rotating device for parallellyadvancing/rotating the LED display; and a video feeding device forfeeding a video signal to the LED display.
 22. A three-dimensionaldisplay as claimed in claim 12, wherein the second means comprises: afilm having a two-dimensional image recorded therein or two-dimensionaldisplay; an image transforming optical system having a prism or mirror;and a projection drum.
 23. A three-dimensional display as claimed inclaim 12, wherein the second means comprises: a two-dimensional display;an optical system; a varifocal lens having a variable focal length; adriving device for driving the varifocal lens; and a synchronizingdevice for synchronizing a change in the focal length of the varifocallens with the displaying of an image of the two-dimensional display. 24.A three-dimensional display as claimed in claim 12, wherein the secondmeans successively switches the two-dimensional images generated by thefirst means to generate a moving three-dimensional image.
 25. Athree-dimensional display as claimed in claim 24, wherein when thetwo-dimensional images generated by the first means include a pluralityof images of an object moving in a direction of depth and the object ismoving toward the observer, the third means progressively raises thebrightness levels of the object images displayed on the plurality ofimage planes toward an image plane close to the observer andprogressively lowers the brightness levels of the object images towardan image plane remote from the observer in synchronism with thesuccessive switching of the two-dimensional images by the second means,and wherein when the object is moving away from the observer, the thirdmeans progressively lowers the brightness levels of the object imagesdisplayed on the plurality of image planes toward an image plane closeto the observer and progressively raises the brightness levels of theobject images toward an image plane remote from the observer insynchronism with the successive switching of the two-dimensional imagesby the second means.
 26. A three-dimensional display as claimed in claim12, wherein the colors of the plurality of two-dimensional objects to bepresented in the two-dimensional images are different each other, thecolor of a three-dimensional object to be represented is determined tothe different colors and the colors of the plurality of thetwo-dimensional objects is possible to change without changing thedetermined color which is viewed by the observer.
 27. Athree-dimensional representation method comprising the steps of:generating two-dimensional images by in which an object is projectedalong the line of sight of an observer, onto a plurality of image planeslocated at different depth positions as seen from an observer; changingbrightness levels of the generated two-dimensional images and displayingthem on the respective image planes; and detecting the movement of aviewing point of the observer in longitudinal, horizontal and verticaldirections to change the two-dimensional images displayed on respectivedisplays according to the detected movement of the viewing point.
 28. Athree-dimensional representation method as claimed in claim 27, whereinthe displays displaying the plurality of two-dimensional images areparallelly moved according to the movement of the viewing point of theobserver.
 29. A three-dimensional representation method as claimed inclaim 27, wherein, according to the movement of the viewing point of theobserver, the plurality of two-dimensional images are rewritten intoimages as they will appear when viewed from the direction of theobserver.
 30. A three-dimensional representation method comprising thesteps of: generating two-dimensional images in which an object isprojected along the line of sight of an observer, onto a plurality ofimage planes located at different depth positions as seen from anobserver; distributing the generated two-dimensional images torespective displays and changing brightness levels of thetwo-dimensional images according to depth positions where thetwo-dimensional images are to be displayed, and displaying them on therespective image planes; and detecting the movement of a viewing pointof the observer in longitudinal, horizontal and vertical directions tochange the two-dimensional images displayed on the respective displaysaccording to the detected movement of the viewing point.
 31. Athree-dimensional representation method as claimed in claim 27, wherein,according to the movement of the viewing point of the observer, theplurality of two-dimensional images are subjected to one or more oftransformation processing including parallel movement, enlargement andreduction.
 32. A three-dimensional display comprising: a two-dimensionalimage generating device for generating two-dimensional images in whichan object is projected along the line of sight of an observer, onto aplurality of image planes located at different positions as seen fromthe observer; a brightness level changing device for changing brightnesslevels of the two-dimensional images and displaying them on the imageplanes; a viewing point movement detecting device for detecting themovement of a viewing point of the observer in longitudinal, horizontaland vertical directions; a two-dimensional image transformation devicefor changing the two-dimensional images according to the detectedmovement of the viewing point; and displays for displaying thetransformed two-dimensional images.
 33. A three-dimensional display asclaimed in claim 32, wherein the two-dimensional image transformationdevice has one or more of transformation processing means for parallellymoving, enlarging and reducing the plurality of two-dimensional imagesaccording to the movement of the viewing point of the observer.
 34. Athree-dimensional display as claimed in claim 32, further including ameans for parallelly moving the displays for displaying the plurality oftwo-dimensional images according to the movement of the viewing point ofthe observer.
 35. A three-dimensional display comprising: atwo-dimensional image generating device for generating two-dimensionalimages in which an object is projected along the line of sight of anobserver, onto a plurality of image planes located at differentpositions as seen from the observer; a distribution device fordistributing the generated two-dimensional images to displays accordingto depth positions where the two-dimensional images are to be displayed,the displays corresponding to the respective depth positions; abrightness level changing device for changing brightness levels of thetwo-dimensional images and displaying them on the image planes; aviewing point movement detecting device for detecting the movement of aviewing point of the observer in longitudinal, horizontal and verticaldirections; a two-dimensional image transformation device for changingthe two-dimensional images according to the detected movement of theviewing point; and displays for displaying the transformedtwo-dimensional images.
 36. A three-dimensional display as claimed inclaim 32, wherein the viewing point movement detecting device comprisesone or more of an infrared sensor, an ultrasonic sensor, a laserdistance sensor, an optical sensor, a camera image-based positiondetection, and a magnetic sensor.
 37. A three-dimensional representationmethod which generates a three-dimensional image in which an object tobe presented onto planes is projected along the line of sight of anobserver, by displaying the two-dimensional images on a plurality ofimage planes simultaneously and at desired brightness levels, theplurality of image planes being located at different depth positions,the three-dimensional representation method comprising the steps of:selecting one of the plurality of objects when the object to bepresented comprises a plurality of objects having different depthpositions; generating two-dimensional images by in which the selectedobject is projected onto planes along the line of sight of the observer;displaying the generated two-dimensional images on the plurality ofimage planes simultaneously; and repeating the above three steps for allof the plurality of objects within an after image time of human eye tosuccessively display three-dimensional images of the plurality ofobjects on a time division basis within the after image time of humaneye. 38 A three-dimensional representation method as claimed in claim37, wherein when the two-dimensional images are displayed on theplurality of image planes simultaneously for a plurality of objects, thebrightness levels of the two-dimensional images displayed on the imageplanes are changed to desired brightness levels individually for eachtwo-dimensional image.
 39. A three-dimensional representation method asclaimed in claim 37, wherein the brightness levels of the plurality ofimage planes are changed periodically; in synchronism with thebrightness levels of the image planes becoming desired levels, an objectis selected from the plurality of objects of two-dimensional images tobe displayed at the desired brightness levels and the two-dimensionalimages of the selected object are displayed on the plurality of imageplanes simultaneously; and this process is performed successively.
 40. Athree-dimensional display comprising: a two-dimensional image generatingmeans for generating two-dimensional images in which one object of aplurality of objects to be presented, the plurality of objects havingdifferent depth positions, is selected one by one and selected object isprojected onto the planes along the line of sight of an observer; adisplay means for displaying the two-dimensional images generated by thetwo-dimensional image generating means simultaneously on a plurality ofimage planes for one selected object after another, the image planesbeing located at different depth positions as seen from the observer,the display means being adapted to repetitively display all of thetwo-dimensional images generated by the two-dimensional image generatingmeans successively within an after image time of human eye; and abrightness level adjusting means for adjusting brightness levels of thetwo-dimensional images displayed on the image planes of the displaymeans in synchronism with the displaying of the two-dimensional imageson the image planes of the display means.
 41. A three-dimensionaldisplay as claimed in claim 40, wherein the brightness level adjustingmeans changes the brightness level periodically and, in synchronism withthe brightness level being changed by the brightness level adjustingmeans, the two-dimensional image generating means selects an object fromthe plurality of objects of two-dimensional images to be displayed atdesired brightness levels, and generates the two-dimensional images ofthe selected object.
 42. A three-dimensional display as claimed in claim40, wherein the two-dimensional image generating means selects oneobject after another from the plurality of objects in a predeterminedorder and generates two-dimensional images of the selected object, andthe brightness level adjusting means changes the brightness level insynchronism with the two-dimensional images being generated by thetwo-dimensional image generating means.
 43. A three-dimensional displaycomprising: a two-dimensional image generating means for generatingtwo-dimensional images in which one object of a plurality of objects tobe presented is selected one by one the plurality of objects havingdifferent depth positions, and the selected object is projected on tothe planes along the line of sight of an observer; and a display meansfor displaying the two-dimensional images generated by thetwo-dimensional image generating means simultaneously on a plurality ofimage planes at predetermined brightness levels for one selected objectafter another, the image planes being located at different depthpositions as seen from the observer, the display means being adapted torepetitively display all of the two-dimensional images generated by thetwo-dimensional image generating means successively within an afterimage time of human eye; wherein the display means includes: atwo-dimensional display means located at each image plane to displaytwo-dimensional images generated by the two-dimensional image generatingmeans; and a brightness level adjusting means disposed in front of thetwo-dimensional display means.
 44. A three-dimensional display asclaimed in claim 43, wherein the brightness level adjusting meanschanges the brightness level periodically and, in synchronism with thebrightness level being changed by the brightness level adjusting means,the two-dimensional image generating means selects an object from theplurality of objects to be presented at desired brightness level, andgenerates the two-dimensional images for the selected object.
 45. Athree-dimensional display as claimed in claim 43, wherein thetwo-dimensional image generating means selects one object after anotherfrom the plurality of objects in a predetermined order and generatestwo-dimensional images for the selected object, and the brightness leveladjusting means changes the brightness level in synchronism with thetwo-dimensional images being generated by the two-dimensional imagegenerating means.
 46. A three-dimensional display as claimed in claim43, wherein the brightness level adjusting means is a beam attenuatingfilter.
 47. A three-dimensional display as claimed in claim 46, whereinthe beam attenuating filter is either a rotary filter which continuouslychanges light intensity attenuation, a filter that rotates a pluralityof slits, a filter that changes an interruption/transmission time by ashutter, or a filter that changes a number of times ofinterruptions/transmissions by a shutter.
 48. A three-dimensionaldisplay as claimed in claim 43, wherein the two-dimensional displaymeans is a display which can randomly access pixels.
 49. Athree-dimensional display comprising: a two-dimensional image generatingmeans for generating two-dimensional images in which one object of aplurality of objects is selected one by one, the plurality of objectshaving different depth positions, and the selected object is projectedon to the planes along the line of sight of an observer; and a displaymeans for displaying the two-dimensional images generated by thetwo-dimensional image generating means simultaneously on a plurality ofimage planes at predetermined brightness levels for one selected objectafter another, the image planes being located at different depthpositions as seen from the observer, the display means being adapted torepetitively display all of the two-dimensional images generated by thetwo-dimensional image generating means successively within an afterimage time of human eye; wherein the display means includes: a pluralityof two-dimensional display means located at each image plane to displaypredetermined two-dimensional images of a plurality of two-dimensionalimages generated by the two-dimensional image generating means; and abrightness level adjusting means disposed in front of the plurality oftwo-dimensional display means.
 50. A three-dimensional display asclaimed in claim 49, wherein the brightness level adjusting meanschanges the brightness level periodically and, in synchronism with thebrightness level being changed by the brightness level adjusting means,the two-dimensional image generating means selects an object from theplurality of objects to be objected at desired brightness level, andgenerates the two-dimensional images for the selected object.
 51. Athree-dimensional display as claimed in claim 49, wherein thetwo-dimensional image generating means selects one object after anotherfrom the plurality of objects in a predetermined order and generatestwo-dimensional images of the selected object, and the brightness leveladjusting means changes the brightness levels in synchronism with thetwo-dimensional images being generated by the two-dimensional imagegenerating means.
 52. A three-dimensional display as claimed in claim51, wherein the two-dimensional display means are a plurality ofprojectors, and the display means further includes screens provided onefor each image plane on which the two-dimensional images are projectedfrom the plurality of projectors.
 53. A three-dimensional display asclaimed in claim 51, wherein the brightness level adjusting means is abeam attenuating filter.
 54. A three-dimensional display as claimed inclaim 53, wherein the beam attenuating filter is either a rotary filterwhich continuously changes light intensity attenuation, a filter thatrotates a plurality of slits, a filter that changes aninterruption/transmission time by a shutter, or a filter that changes anumber of times of interruptions/transmissions by a shutter.
 55. Athree-dimensional display as claimed in claim 51, wherein thetwo-dimensional display means are displays which can randomly accesspixels.
 56. A three-dimensional display comprising: a two-dimensionalimage generating means for generating two-dimensional images in whichone object of a plurality of objects is selected one by one, theplurality of objects having different depth positions, the selectedobject is projected on to along the line of sight of an observer; and adisplay means for displaying the two-dimensional images generated by thetwo-dimensional image generating means simultaneously on a plurality ofimage planes at predetermined brightness levels for one selected objectafter another, the image planes being located at different depthpositions as seen from the observer, the display means being adapted torepetitively display all of the two-dimensional images generated by thetwo-dimensional image generating means successively within an afterimage time of human eye; wherein the display means includes: atwo-dimensional display means located at each image plane to displaytwo-dimensional images generated by the two-dimensional image generatingmeans at the predetermined brightness levels.
 57. A three-dimensionaldisplay as claimed in claim 56, wherein the two-dimensional displaymeans changes the brightness level periodically and, in synchronism withthe brightness level being changed by the two-dimensional display means,the two-dimensional image generating means selects an object from theplurality of objects which has two-dimensional images to be displayed atdesired brightness levels, and generates the two-dimensional images ofthe selected object.
 58. A three-dimensional display as claimed in claim56, wherein the two-dimensional image generating means selects oneobject after another from the plurality of objects in a predeterminedorder and generates two-dimensional images of the selected object, andthe two-dimensional display means changes the brightness level insynchronism with the two-dimensional images being generated by thetwo-dimensional image generating means.
 59. A three-dimensional displayas claimed in claim 56, wherein the two-dimensional display means is adisplay which can randomly access pixels.
 60. A three-dimensionaldisplay comprising: a two-dimensional image generating means forgenerating two-dimensional images in which one object after of aplurality of objects is selected one by one, the plurality of objectshaving different depth positions, and selected object is projected on tothe planes along the line of sight of an observer; and a display meansfor displaying the two-dimensional images generated by thetwo-dimensional image generating means simultaneously on a plurality ofimage planes at predetermined brightness levels for one selected objectafter another, the image planes being located at different depthpositions as seen from the observer, the display means being adapted torepetitively display all of the two-dimensional images generated by thetwo-dimensional image generating means successively within an afterimage time of human eye; wherein the display means includes: a pluralityof two-dimensional display means located at each image plane to displayat predetermined brightness levels predetermined two-dimensional imagesof a plurality of two-dimensional images generated by thetwo-dimensional image generating means.
 61. A three-dimensional displayaccording to claim 60, wherein the two-dimensional display means changesthe brightness level periodically and, in synchronism with thebrightness level being changed by the two-dimensional display means, thetwo-dimensional image generating means selects an object from theplurality of objects which has two-dimensional images to be displayed atdesired brightness levels, and generates the two-dimensional images ofthe selected object.
 62. A three-dimensional display according to claim60, wherein the two-dimensional image generating means selects oneobject after another from the plurality of objects in a predeterminedorder and generates two-dimensional images for the selected object, andthe two-dimensional display means changes the brightness levels insynchronism with the two-dimensional images being generated by thetwo-dimensional image generating means.
 63. A three-dimensional displayaccording to claim 60, wherein the two-dimensional display means is adisplay which can randomly access pixels.
 64. In a three-dimensionalrepresentation method which generates a three-dimensional image bydisplaying the two-dimensional images on all of a plurality of imageplanes at desired brightness levels, an object to be presented oftwo-dimensional images being projected on to the planes, and within anafter image time of human eye, the plurality of image planes beinglocated at different depth positions, the three-dimensionalrepresentation method comprising the steps of: controlling apolarization direction of display light of the two-dimensional images;and passing the display light through an optical system that hasdifferent focusing positions according to the polarization direction ofthe passing display light so that the display light of thetwo-dimensional images is focused on the plurality of image planeslocated at different depth positions to display the two-dimensionalimages on the plurality of image planes located at different depthpositions.
 65. A three-dimensional representation method as claimed inclaim 64, wherein while the two-dimensional images are successivelyswitched, the polarization direction of the display light of thetwo-dimensional images is successively switched to focus the displaylight of the two-dimensional images on the plurality of image planeslocated at different depth positions to generate a three-dimensionalmoving image.
 66. A three-dimensional representation method as claimedin claim 64, wherein, in synchronism with the successive switching ofthe polarization direction of the display light of the two-dimensionalimages, the brightness levels of the display light of thetwo-dimensional images are changed to desired brightness levels.
 67. Athree-dimensional representation method as claimed in claim 65, whereinthe polarization direction of the display light of the two-dimensionalimages is controlled to adjust to desired levels the brightness levelsof the two-dimensional images focused on the plurality of image planeslocated at different depth positions.
 68. A three-dimensional displaycomprising: a two-dimensional image display means for displayingtwo-dimensional images; a polarization varying means for controlling apolarization direction of display light of the two-dimensional imagesentering from the two-dimensional image display means and thenoutputting the display light; and a polarization type bifocal opticalsystem for splitting the display light exiting from the polarizationvarying means into two independent polarization directions and focusingthe two independent polarization direction beams on two different imageplanes; wherein the two-dimensional image display means, thepolarization varying means and the polarization type bifocal opticalsystem are arranged so that the two-dimensional images focused on thetwo different image planes overlap each other on the line of sight of anobserver and have different depth positions.
 69. A three-dimensionaldisplay as claimed in claim 68, wherein the two-dimensional imagedisplay means changes brightness levels of the two-dimensional images insynchronism with the changing of the polarization direction by thepolarization varying means.
 70. A three-dimensional display as claimedin claim 68, wherein the polarization varying means changes the displaylight of the two-dimensional images entering from the two-dimensionalimage display means into elliptically polarized light.
 71. Athree-dimensional display as claimed in claim 68, wherein thepolarization varying means changes the display light of thetwo-dimensional images entering from the two-dimensional image displaymeans into linearly polarized light having the two independentpolarization directions split by the polarization type bifocal opticalsystem or an intermediate polarization angle between the two independentpolarization directions.
 72. A three-dimensional display as claimed inclaim 68, wherein the polarization varying means includes a medium whosebirefringence is changed by application of electric field or voltage.73. A three-dimensional display as claimed in claim 68, wherein themedium whose birefringence is changed, is a liquid crystal.
 74. Athree-dimensional display as claimed in claim 68, wherein thetwo-dimensional image display means has a plurality of pixels, thepolarization varying means has a plurality of polarization varyingelements, and each of the polarization varying elements of thepolarization varying means controls polarization of display light of oneor more pixels of the two-dimensional image display means.
 75. Athree-dimensional display as claimed in claim 68, wherein thepolarization type bifocal optical system includes a fixed focus lens ofan isotropic medium and a birefringent medium.
 76. A three-dimensionaldisplay as claimed in claim 68, wherein the polarization type bifocaloptical system includes a lens-shaped birefringent medium.
 77. Athree-dimensional display as claimed in claim 75, wherein thebirefringent medium is a liquid crystal.
 78. A three-dimensional displayas claimed in claim 68, wherein the polarization type bifocal opticalsystem includes: a first polarizing beam splitter for splitting thedisplay light output from the polarization varying means into twoindependent polarization directions; two optical systems passing the twosplit display beams separated by the first polarizing beam splitter andhaving different image focusing positions; and a second polarizing beamsplitter for synthesizing the two split display beams that have passedthrough the two optical systems.
 79. A three-dimensional display asclaimed in claim 78, wherein the first or second polarizing beamsplitter is replaced with two polarizing plates having polarizationdirections different from that of the beam splitter.
 80. Athree-dimensional representation method which generates athree-dimensional image by arranging a plurality of image planes atdifferent depth positions for each of left and right eyes of an observerand by displaying two-dimensional images on the plurality of imageplanes for each of the left and right eyes of the observer, thethree-dimensional representation method comprising the steps of:generating two-dimensional images in which an object to be presented isprojected from a point on a line passing through the left and right eyesof the observer onto the plurality of image planes; changing brightnesslevels of the generated two-dimensional images individually for eachimage plane for the left eye and for the right eye of the observer; anddisplaying the generated two-dimensional images on the plurality ofimage planes for the left eye and for right eye of the observer.
 81. Athree-dimensional representation method as claimed in claim 80, wherein,when the object to be presented is displayed at a depth position closeto the observer, the brightness levels of the two-dimensional imagesdisplayed on those image planes of the plurality of image planes whichare close to the observer are raised and the brightness levels of thetwo-dimensional images displayed on the image planes remote from theobserver are lowered, and wherein, when the object to be presented isdisplayed at a depth position remote from the observer, the brightnesslevels of the two-dimensional images displayed on those image planes ofthe plurality of image planes which are close to the observer arelowered and the brightness levels of the two-dimensional imagesdisplayed on the image planes remote from the observer are raised.
 82. Athree-dimensional representation method as claimed in claim 81, whereinthe two-dimensional images are displayed on the plurality of imageplanes so that they overlap each other when seen from one point on aline passing through the left and right eyes of the observer, and thebrightness levels of the two-dimensional images displayed on theplurality of image planes are changed so that an overall brightnesslevel as seen by the observer is equal to the brightness level of theoriginal object to be presented.
 83. A three-dimensional representationmethod as claimed in claim 80, wherein the two-dimensional images aredisplayed on the plurality of image planes so that they overlap eachother when seen from one point on a line passing through the left andright eyes of the observer, and the brightness levels of each part ofthe two-dimensional images displayed on the plurality of image planesare changed according to the depth position of the original object to bepresented so that an overall brightness level as seen by the observer isequal to the brightness level of the object to be presented.
 84. Athree-dimensional representation method as claimed in claim 80, whereinthe two-dimensional images are successively switched to generate athree-dimensional moving image.
 85. A three-dimensional representationmethod as claimed in claim 84, wherein when the two-dimensional imagesinclude a plurality of images of an object moving in a direction ofdepth and the object is moving toward the observer, the brightnesslevels of the object images displayed on the plurality of image planesare progressively raised from an image plane remote from the observertoward an image plane close to the observer in synchronism with thesuccessive switching of the two-dimensional images, and wherein when thetwo-dimensional images include a plurality of images of an object movingin a direction of depth and the object is moving away from the observer,the brightness levels of the object images displayed on the plurality ofimage planes are progressively raised from an image plane close to theobserver toward an image plane remote from the observer in synchronismwith the successive switching of the two-dimensional images.
 86. Ahead-mounted display for displaying a three-dimensional image bydisplaying two-dimensional images on a plurality of image planes locatedat different depth positions as seen by an observer, the head-mounteddisplay comprising: a first means for fixing relative positions betweenthe plurality of image planes and left and right eyes of the observer; asecond means for generating two-dimensional images in which an object tobe presented from one point on a line passing through the left and righteyes of the observer onto the plurality of image planes; a third meansfor displaying the two-dimensional images generated by the imagegenerating means on at least two of the plurality of image planes; and afourth means for changing brightness levels of the two-dimensionalimages displayed on the at least two image planes individually for eachimage plane.
 87. A head-mounted display as claimed in claim 86, whereinthe third means comprises: a plurality of two-dimensional displays; atotal reflecting mirror or partial reflecting mirror combined with oneof the plurality of two-dimensional displays which is located at theremotest depth position from the observer, the total reflecting mirroror partial reflecting mirror being adapted to locate an image of the onetwo-dimensional display on the line of sight of the observer; andpartial reflecting mirrors combined with the two-dimensional displaysexcept for the one two-dimensional display located at the remotest depthposition from the observer, the partial reflecting mirrors being adaptedto locate images of the two-dimensional displays on the line of sight ofthe observers.
 88. A head-mounted display as claimed in claim 86,wherein the third means comprises: a plurality of two-dimensionaldisplays; a combination of a total reflecting mirror and a lens or acombination of a partial reflecting mirror and a lens, the combinationbeing combined with one of the plurality of two-dimensional displayswhich is located at the remotest depth position from the observer, thecombination being adapted to locate an image of the one two-dimensionaldisplay on the line of sight of the observer; and combinations ofpartial reflecting mirrors and lenses, the combinations being combinedwith the two-dimensional displays except for the one two-dimensionaldisplay located at the remotest depth position from the observer, thecombinations being adapted to locate images of the two-dimensionaldisplays on the line of sight of the observer.
 89. A head-mounteddisplay as claimed in claim 86, wherein the third means comprises: aplurality of scatter plates capable of controlling a switching between atransmitting state and a scattering state, the scatter plates beinglocated at different depth positions as viewed from the observer; aplurality of projection type two-dimensional displays for projectingtwo-dimensional images onto the plurality of scatter plates; and aplurality of shutters disposed between the plurality of scatter platesand the plurality of projection type two-dimensional displays, theplurality of shutters being adapted to switch between a transmittingstate and a cutoff state in synchronism with the switching between thetransmitting state and the scattering state of the plurality of scatterplates.
 90. A head-mounted display as claimed in claim 86, wherein alens optical system is disposed between the plurality of image planesand the observer.
 91. A head-mounted display as claimed in claim 86,wherein, when the object to be presented is displayed at a depthposition close to the observer, the fourth means raises the brightnesslevels of the two-dimensional images displayed on those image planes ofthe plurality of image planes which are close to the observer and lowersthe brightness levels of the two-dimensional images displayed on theimage planes remote from the observer, and wherein, when the object tobe presented is displayed at a depth position remote from the observer,the fourth means lowers the brightness levels of the two-dimensionalimages displayed on those image planes of the plurality of image planeswhich are close to the observer and raises the brightness levels of thetwo-dimensional images displayed on the image planes remote from theobserver.
 92. A head-mounted display as claimed in claim 86, wherein thethird means displays the two-dimensional images on the plurality ofimage planes so that they overlap each other when viewed from one pointon a line passing through the left and right eyes of the observer, andthe fourth means changes the brightness levels of the two-dimensionalimages displayed on the plurality of image planes so that an overallbrightness level as seen by the observer is equal to the brightnesslevel of the original object to be presented.
 93. A head-mounted displayas claimed in claim 86, wherein the third means displays thetwo-dimensional images on the plurality of image planes so that theyoverlap each other when viewed from one point on a line passing throughthe left and right eyes of the observer, and the fourth means changesthe brightness levels of each part of the two-dimensional imagesdisplayed on the plurality of image planes according to the depthposition of the original object to be presented so that an overallbrightness level as seen by the observer is equal to the brightnesslevel of the object to be presented.
 94. A head-mounted display asclaimed in claim 86, wherein the third means successively switches anddisplays the two-dimensional images generated by the image generatingmeans to display a three-dimensional moving image.
 95. A head-mounteddisplay as claimed in claim 94, wherein when the two-dimensional imagesgenerated by the first means include a plurality of images of an objectmoving in a direction of depth and the object is moving toward theobserver, the fourth means progressively raises the brightness levels ofthe object images displayed on the plurality of image planes from animage plane remote from the observer toward an image plane close to theobserver in synchronism with the successive switching of thetwo-dimensional images by the third means, and wherein when the objectis moving away from the observer, the fourth means progressively raisesthe brightness levels of the object images displayed on the plurality ofimage planes from an image plane close to the observer toward an imageplane remote from the observer in synchronism with the successiveswitching of the two-dimensional images by the third means.
 96. Ahead-mounted display for displaying a three-dimensional image bydisplaying two-dimensional images on a plurality of image planes locatedat different depth positions as seen from a left eye of an observer andon a plurality of image planes located at different depth positions asseen from a right eye of the observer, the head-mounted displaycomprising: a first means for fixing relative positions between theplurality of image planes for the left eye and the left eye of theobserver and between the plurality of image planes for the right eye andthe right eye of the observer; a second means for generatingtwo-dimensional images in which an object to be projected from one pointon a line passing through the left and right eyes of the observer ontothe plurality of image planes for the left eye and for the right eye; athird means for displaying the two-dimensional images generated by theimage generating means on at least two of the plurality of image planesfor the left eye and for the right eye; and a fourth means for changingbrightness levels of the two-dimensional images displayed on the atleast two image planes individually at least two image planes at a timefor the left eye and for the right eye.
 97. A head-mounted display asclaimed in claim 96, wherein the third means comprises: a plurality oftwo-dimensional displays; a total reflecting mirror or partialreflecting mirror combined with one of the plurality of two-dimensionaldisplays which is located at the remotest depth position from theobserver, the total reflecting mirror or partial reflecting mirror beingadapted to locate an image of the one two-dimensional display on theline of sight of the observer; and partial reflecting mirrors combinedwith the two-dimensional displays except for the one two-dimensionaldisplay located at the remotest depth position from the observer, thepartial reflecting mirrors being adapted to locate images of thetwo-dimensional displays on the line of sight of the observers.
 98. Ahead-mounted display as claimed in claim 96, wherein the third meanscomprises: a plurality of two-dimensional displays; a combination of atotal reflecting mirror and a lens or a combination of a partialreflecting mirror and a lens, the combination being combined with one ofthe plurality of two-dimensional displays which is located at theremotest depth position from the observer, the combination being adaptedto locate an image of the one two-dimensional display on the line ofsight of the observer; and combinations of partial reflecting mirrorsand lenses, the combinations being combined with the two-dimensionaldisplays except for the one two-dimensional display located at theremotest depth position from the observer, the combinations beingadapted to locate images of the two-dimensional displays on the line ofsight of the observer.
 99. A head-mounted display as claimed in claim96, wherein the third means comprises: a plurality of scatter platescapable of controlling a switching between a transmitting state and ascattering state, the scatter plates being located at different depthpositions as viewed from the observer; a plurality of projection typetwo-dimensional displays for projecting two-dimensional images onto theplurality of scatter plates; and a plurality of shutters disposedbetween the plurality of scatter plates and the plurality of projectiontype two-dimensional displays, the plurality of shutters being adaptedto switch between a transmitting state and a cutoff state in synchronismwith the switching between the transmitting state and the scatteringstate of the plurality of scatter plates.
 100. A head-mounted display asclaimed in claim 89, wherein a lens optical system is disposed betweenthe plurality of image planes and the observer.
 101. A head-mounteddisplay as claimed in claim 96, wherein, when the object to be presentedis displayed at a depth position close to the observer, the fourth meansraises the brightness levels of the two-dimensional images displayed onthose image planes of the plurality of image planes which are close tothe observer and lowers the brightness levels of the two-dimensionalimages displayed on the image planes remote from the observer, andwherein, when the object to be presented is displayed at a depthposition remote from the observer, the fourth means lowers thebrightness levels of the two-dimensional images displayed on those imageplanes of the plurality of image planes which are close to the observerand raises the brightness levels of the two-dimensional images displayedon the image planes remote from the observer. 102 A head-mounted displayas claimed in claim 96, wherein the third means displays thetwo-dimensional images on the plurality of image planes so that theyoverlap each other when viewed from one point on a line passing throughthe left and right eyes of the observer, and the fourth means changesthe brightness levels of the two-dimensional images displayed on theplurality of image planes so that an overall brightness level as seen bythe observer is equal to the brightness level of the original object tobe presented.
 103. A head-mounted display as claimed in claim 96,wherein the third means displays the two-dimensional images on theplurality of image planes so that they overlap each other when viewedfrom one point on a line passing through the left and right eyes of theobserver, and the fourth means changes the brightness levels of eachpart of the two-dimensional images displayed on the plurality of imageplanes according to the depth position of the original object to bepresented so that an overall brightness level as seen by the observer isequal to the brightness level of the object to be presented.
 104. Ahead-mounted display as claimed in claim 96, wherein the third meanssuccessively switches the two-dimensional images generated by the imagegenerating means to display a two-dimensional moving image.
 105. Ahead-mounted display as claimed in claim 104, wherein when thetwo-dimensional images generated by the first means include a pluralityof images of an object moving in a direction of depth and the object ismoving toward the observer, the fourth means progressively raises thebrightness levels of the object images displayed on the plurality ofimage planes from an image plane remote from the observer toward animage plane close to the observer in synchronism with the successiveswitching of the two-dimensional images by the third means, and whereinwhen the object is moving away from the observer, the fourth meansprogressively raises the brightness levels of the object imagesdisplayed on the plurality of image planes from an image plane close tothe observer toward an image plane remote from the observer insynchronism with the successive switching of the two-dimensional imagesby the third means.
 106. A three-dimensional display comprising: athree-dimensional display means having a plurality of two-dimensionaldisplays located at different depth positions, the three-dimensionaldisplay means being adapted to present a three-dimensional image bydisplaying an object to be presented on image planes of the plurality oftwo-dimensional displays and by variably setting a brightness levelratio of the plurality of two-dimensional displays according to a depthposition of the object to be presented; and a viewing zone distributingmeans for distributing a viewing zone of the three-dimensional displaymeans into a plurality of directions.
 107. A three-dimensional displayas claimed in claim 106, wherein the viewing zone distributing meansexpands the viewing zone by distributing the viewing zone.
 108. Athree-dimensional display as claimed in claim 106, wherein the viewingzone distributing means increases the number of viewing zones bydistributing the viewing zone.
 109. A three-dimensional display asclaimed in claim 106, wherein the viewing zone distributing means has anoptical system including either a plurality of total reflecting mirrorsor a plurality of prisms, or a combination of these, and reflects orrefracts light by the optical system to distribute the viewing zone.110. A three-dimensional display as claimed in claim 106, wherein theviewing zone distributing means has an optical system including aplurality of dichroic mirrors or dichroic prisms with differentreflection wavelength bands or a combination of these, and reflects orrefracts light by the optical system to distribute the viewing zone.111. A three-dimensional display as claimed in claim 106, wherein theviewing zone distributing means has an optical system including aholographic optical element with a plurality of reflection angles ordiffraction angles, a holographic optical element with a singlereflection angle or diffraction angle, or a combination of these, andthe viewing zone distributing means reflects or diffracts light by theoptical system to distribute the viewing zone.
 112. A three-dimensionaldisplay as claimed in claim 106, wherein the viewing zone distributingmeans includes a prism array having an array of prisms with differentrefraction directions, and refracts light by the prism array todistribute the viewing zone.
 113. A three-dimensional display as claimedin claim 106, wherein the viewing zone distributing means includes amirror array having arrays of mirrors with different reflectiondirections, and reflects light by the mirror array to distribute theviewing zone.
 114. A three-dimensional display as claimed in claim 106,wherein the viewing zone distributing means includes a diffractiongrating array having arrays of diffraction gratings with differentdiffraction angles, and reflects or diffracts light by the diffractiongrating array to distribute the viewing zone.
 115. A three-dimensionaldisplay according to claim 106, wherein the viewing zone distributingmeans includes a liquid crystal deflection element having a liquid andan optical element disposed in contact with the liquid crystal, andrefracts or reflects light by the liquid crystal deflection element todistribute the viewing zone on a time division basis.
 116. Athree-dimensional display as claimed in claim 107, wherein the viewingzone distributing means includes a movable optical system and a shutterdevice for performing shutter operations, the movable optical systembeing either half mirrors, total reflecting mirrors or prisms, or acombination of these, and wherein the viewing zone distributing meansdistributes the viewing zone on a time division basis by arranging theshutter device between the three-dimensional display and the opticalsystem, reflecting or refracting light by the optical system andsynchronizing the three-dimensional display with the shutter device.117. A three-dimensional display as claimed in claim 106, wherein theviewing zone distributing means includes a movable optical system, whichis either half mirrors, total reflection mirrors or prisms, or acombination of these, and the viewing zone distributing means operatesthe optical system stepwise to reflect or refract light and therebydistribute the viewing zone on a time division basis.